[whyzee125]

Originally Posted by jzx_andy

OP, I'm sorry that this has resulted in a fail in your case.

What other mods do you have? While NVH is subjective, I find the question of how "noticeable" NVH from mods is highly dependent what you've done (or what you haven't done) to the rest of the car.

If your car is completely stock, oem exhaust, mounts, factory clutch etc, I would think some people would find certain mods almost intolerable in terms of NVH, due to how quiet a factory specification e9x is overall. Just imagine a bone stock e9x with upgraded engine mounts, it'd probably feel like something's out of place since the vehicle will really only resonate a lot of NVH while idling, and completely goes away the moment you accelerate/cruise. On the other hand, that sort of NVH would feel more "natural" on a car that's gone the whole 9 yards with a louder exhaust, rear end, tyres, etc. In the latter case, the vehicle would be louder than a stock e9x under all conditions - idle, load, cruising at speed, etc, but the noise wouldn't be coming from one area.

I would presume you perceive subtle changes in NVH quite well and/or have a very tame example of an E9x, given that you refer to all season street tyres as being "a little noisy". There is nothing wrong with this perception, though it is a useful reference point for when NVH becomes noticeable in your specific case.

That said, a lot of people who go for solid subframe bushings would have already done various other modifications that each increase NVH in their own way, such as an aftermarket exhaust, single mass flywheel, engine mounts, trans mounts rear shock mounts, coilovers, larger wheels, dual use road+track tyres, etc. These other modifications coupled together help to balance and, in effect, drown out NVH that's coming from one specific source.

I opted for PLM solid subframe bushings on a car that sees street use 99% of the time. I fitted them shortly after having done a bunch of other upgrades, inclusive of poly engine mounts (which I found add a noticeable amount of NVH and would recommend against from a cost vs benefit vs comfort analysis). The only item I've left alone at this point is the factory catback. All that said, I found the NVH increase from solid subframe bushings to be minimal and I'm ok with the upgrade.

Do let us know how you fare once you've replaced them for something else. All the best.

Thanks so much for the perspective, and I think you're spot on. My guess is that most people who claim these made no NVH difference are so far down the NVH path that the subframe bushings made little to no additional difference. My car is making 475+whp so I liked the idea of keeping things locked down a bit more as it could be a bit darty at WOT, but just as you suggested, it otherwise drives like a stock car with no real NVH-increasing mods. I'm on KW street comfort coilovers, M3 front control arms with Dinan camber plates and Dinan rear shock mounts. Continental DWS06 tires. Car was quiet as a mouse before.

I'll def keep you posted on the next set--it could be there's something wrong with my car but I suspect it will quiet down a lot once I go with poly or M3 bushings.

[whyzee125]

Originally Posted by carguy138

Heat shield rubbing top of the driveshaft in front of the rear diff? Also take a look at the mounts and make sure the subframe is fully seated on the bushings.

For perspective, I had a BMW PE exhaust and sold it. Found it too loud (even with stock DP). I'm also running the stock dual mass flywheel (manual) and 335is engine mounts. I also found the stock runflats to be way too harsh and ditched those early on for michelin PSS tires.

all mods to give context (car feels like a stock E90 M3 in terms of NVH).
-koni yellows
-dinan springs
-poly front control arm bushings
-UUC front sway bar
-e90 m3 rear swaybar
-e90 m3 front strut tower brace
-e93 m3 rear chassis brace
-turner delrin subframe bushings
-turner delrin rear differential mount bushings (DID ADD NOISE but similar to a stock subaru STI)
-wavetrac LSD
-335is engine mounts
-PSS tires in summer/ blizzaks in winter.
-stock exhaust and stock downpipe.
-335is/550i clutch with DMF
-dinan front camber plates

everything else is stock.

That's funny that you found the PE too loud, as I have that with downpipes and find it barely louder than stock lol! Maybe particular tunes change the loudness some or maybe it really is all perspective. That's a little disconcerting as it sounds like you don't like a lot of NVH either so it's definitely possible my diff is clapped or something. It doesn't sound like a scraping noise at all, like I'd expect a heat shield to if it were rubbing. I've inspected the whole subframe especially near the mounting areas and everything looks perfect. Really odd.

[tylerhart_21]

If the center bearing on the driveshaft is messing up, it will get worse. Mine got bad because it happened during COVID and if you went past barely any throttle it would vibrate the car. It could be also you just needing to change your transmission fluid. I had both at once and it wasn’t fun.

It may because I have a 328i but there alittle diff wine around 45-50 if you are on maintaining the speed. But I can’t remember the rpm and mph. And yes my suspension (m-sport) is stock besides m3 bracing.

I don’t fully understand how the performance exhaust for the 335i worked, but for the 328i. It’s straight though with a center perforated section and no resonator. The 335is is the stock muffler with less stuffing in it.

But overall I would say do your research, ask around, and try it out. That’s how you are going to find the right setup for your car and driving. I can’t speak for any 335’s but for me I am doing an Alpina setup. If anyone is interested I can drop the parts list for it.

[Tambohamilton]

Originally Posted by whyzee125

Nope. Zero change in corners, zero change on/off throttle. No noise while spinning in the air on jacks. Everything is definitely installed correctly too, I've been under there many times. Also changed in frequency significantly when I switched tire brands.

Crazy amount of noise if it's just coming from the tyres... I really feel like something must be up for it to be making that much noise. Even a heat shield buzzing against the centre bearing or something...

[iPee]

whyzee125 have you decided which route you are going to go 95A or M3?

Hoping to see a review either way before I decide. I'm very likely going to go 95A though.

[whyzee125]

Originally Posted by iPee

whyzee125 have you decided which route you are going to go 95A or M3?

Hoping to see a review either way before I decide. I'm very likely going to go 95A though.

I haven't decided for sure but I'm leaning towards the AKG's. I'll definitely report back once I get either set installed!

[cruizinmax]

As another person who's installed solid subframe bushings and experienced minimal NVH changes, there has to be another factor here. Do you have stock diff bushings? Diff brace?

I felt like these bushing helped reduce the "squirm" by 20% or so. The biggest thing that completely eliminated it was coding out the E-diff. I put in a wavetrac and still had it until the coding. It really makes sense if you think about it. The computer is applying the brakes to a wheel that is moving slightly faster taking away the drive from that wheel and sending torque to the opposite wheel. It's intervening much more often than you'd think and it cycles back and forth between the left and right sides multiple times per second. Each time it does this it results in a slight change in the direction of thrust of the rear end. Annoying how there was no LSD option for these cars from the factory.

[Torgus]

Originally Posted by cruizinmax

As another person who's installed solid subframe bushings and experienced minimal NVH changes, there has to be another factor here. Do you have stock diff bushings? Diff brace?

I felt like these bushing helped reduce the "squirm" by 20% or so. The biggest thing that completely eliminated it was coding out the E-diff. I put in a wavetrac and still had it until the coding. It really makes sense if you think about it. The computer is applying the brakes to a wheel that is moving slightly faster taking away the drive from that wheel and sending torque to the opposite wheel. It's intervening much more often than you'd think and it cycles back and forth between the left and right sides multiple times per second. Each time it does this it results in a slight change in the direction of thrust of the rear end. Annoying how there was no LSD option for these cars from the factory.

Yeah I had zero NVH from the install of solid subframe bushings. I have read many other people say the same thing. I saw the video of the OP and it is horrible. I would not drive my car if it sounded like that. I still can't fathom why the massive difference in NVH from one car to another.

I had stock exhaust, stock struts, eibach springs, and a quaiffe diff. No other suspension mods or anything that could effect rear NVH. I did turner solid metal subframe, solid metal differential, and a diff lockdown kit all at the same time. I then coded out E diff. The Ediff should have been coded out when I install the differential but that is another matter. I did gain diff whine above say 50mph.

It added basically zero NVH(other than diff whine above 50mph) but it REALLY firmed up the rear end and made it feel in control and predictable. Before it was kind of squishy if that makes sense.

It is very odd that there is such a huge difference in experience. You can install them wrong but I saw the OPs picture and they looked correct to me with the tabs on the bottom. Very odd. Just does not make sense and it's not that I can handle some huge level of NVH. I saw the video, if it sounded/felt like that I would never drive the car.

[cruizinmax]

Originally Posted by Torgus

Yeah I had zero NVH from the install of solid subframe bushings. I have read many other people say the same thing. I saw the video of the OP and it is horrible. I would not drive my car if it sounded like that. I still can't fathom why the massive difference in NVH from one car to another.

I had stock exhaust, stock struts, eibach springs, and a quaiffe diff. No other suspension mods or anything that could effect rear NVH. I did turner solid metal subframe, solid metal differential, and a diff lockdown kit all at the same time. I then coded out E diff. The Ediff should have been coded out when I install the differential but that is another matter. I did gain diff whine above say 50mph.

It added basically zero NVH(other than diff whine above 50mph) but it REALLY firmed up the rear end and made it feel in control and predictable. Before it was kind of squishy if that makes sense.

It is very odd that there is such a huge difference in experience. You can install them wrong but I saw the OPs picture and they looked correct to me with the tabs on the bottom. Very odd. Just does not make sense and it's not that I can handle some huge level of NVH. I saw the video, if it sounded/felt like that I would never drive the car.

I found the video of the noise. That sounds to me like bad differential bearings. The rubber bushings may have been masking the sound before. Definitely not a normal solid subframe bushing sound.

[carguy138]

Originally Posted by cruizinmax

I found the video of the noise. That sounds to me like bad differential bearings. The rubber bushings may have been masking the sound before. Definitely not a normal solid subframe bushing sound.

+1 That's not a normal sound, something's jacked up.

Wavetrac, solid subframe and differential bushings here. Never sounded like that. Tiny bit of gear whine under acceleration/de-acceleration but only after I installed the solid differential bushings.

[Tambohamilton]

+2 needs a full check over to find that noise before you go switching subframe bushings again...

[whyzee125]

Originally Posted by Tambohamilton

+2 needs a full check over to find that noise before you go switching subframe bushings again...

I definitely don't consider myself an expert mechanic or anything but I'm competent with a wrench and I've been under there multiple times. Can't find any issues at all. All bushings are tight, wheel bearings are quiet on a lift, diff is quiet, CSB is new, and the noise changed 100% in pitch when I swapped tires. I'm positive it's just road noise being transmitted directly into the cabin.

I of course could be wrong but there are multiple sources I trust saying this is normal with these bushings, such as:

https://www.m3post.com/forums/showpo...8&postcount=29

The shop I used also warned me not to do it beforehand due to the completely un-streetable NVH but told them to do it anyway due to the good reviews from everyone on the forums. All this leads me to believe that there's nothing wrong with my car.

I'm also extremely sensitive to any odd noises, rattles, NVH, etc. and the car was completely quiet with the stock bushings.

[335i54n]

i really find that hard to believe that your car wasnt messed up before and the fact it up on a lift and you can bring it to speed and yet still cant locate that noise. gl, eventually whatever bearing making that noise will leave u stranded

[whyzee125]

Originally Posted by 335i54n

i really find that hard to believe that your car wasnt messed up before and the fact it up on a lift and you can bring it to speed and yet still cant locate that noise. gl, eventually whatever bearing making that noise will leave u stranded

Trust me, I would MUCH rather not do the bushings again--I spent almost $1,800 on them and they completely eliminated the squirm under WOT which was the whole point.

The experiences of HPA, the shop I used, and the few others that had this experience + my car being quiet underneath makes me think my car is fine.

I had a bad diff bearing in my 4runner and it took about 10 seconds to find on a lift. It was deafening underneath.

My car is dead quiet underneath, but diagnosing it from halfway across the country over the internet hardly seems scientific either lol

[Tambohamilton]

I have a clunk that sounds like a loose suspension joint on my car. It's been there for about 2.5 years. Been through 2 MOT tests, been to an independent garage, had it on a lift, on jacks on ramps.........can't find it. But I can hear it! I've got to the point of remounting/checking things I don't even think are making the noise - side skirts, trim, seat bases. I hope yours is easier to find than mine.

Another anecdote - I had an intermittent buzz happened about 2k rpm when accelerating, but at no other time. I gave up looking for it in the end. Then I replaced the centre bearing on the driveshaft, and noticed a slight scuff on the heat shield - it had been bent slightly, just enough to buzz the centre bearing at a certain frequency. I bent it down, and no more noise.

I wouldn't be surprised if your noise was caused by a heat shield somewhere - they're super loud in the cab.

[Torgus]

whyzee125 could you post your video again?

[whyzee125]

Originally Posted by Torgus

whyzee125 could you post your video again?

You bet! Brace your ears lol https://www.youtube.com/shorts/m0L3NVsXTG8

[whyzee125]

Originally Posted by Tambohamilton

I have a clunk that sounds like a loose suspension joint on my car. It's been there for about 2.5 years. Been through 2 MOT tests, been to an independent garage, had it on a lift, on jacks on ramps.........can't find it. But I can hear it! I've got to the point of remounting/checking things I don't even think are making the noise - side skirts, trim, seat bases. I hope yours is easier to find than mine.

Another anecdote - I had an intermittent buzz happened about 2k rpm when accelerating, but at no other time. I gave up looking for it in the end. Then I replaced the centre bearing on the driveshaft, and noticed a slight scuff on the heat shield - it had been bent slightly, just enough to buzz the centre bearing at a certain frequency. I bent it down, and no more noise.

I wouldn't be surprised if your noise was caused by a heat shield somewhere - they're super loud in the cab.

I'll definitely get under there again and check that. Weird how it changed with the tires but I've seen a lot of weird things on these cars lol

[Tambohamilton]

Originally Posted by whyzee125

I'll definitely get under there again and check that. Weird how it changed with the tires but I've seen a lot of weird things on these cars lol

I think things like heat shields are just fickle enough that a slight change in input vibration could make them buzz quite differently. Or even jacking and lowering the car upset it enough to change the buzz...

I'd give everything I can touch under there a good shake/thump/wiggle to see if anything makes any unexpected noise. Even give each heat shield a slight bend, in the hope that it even changes the noise and you can narrow down the culprits.

Good luck!

[Torgus]

I was going to suggest a worn guibo but you didn't stiffen up your diff mounts at all and I wouldn't think the subframe could effect that much...but the diff mounts are in the subframe. Maybe the stock rubber subframe inserts hid it? I'm just throwing out an ideas as that video is loud AF.

Did you say it changes for the worse based on RPM or speed again?

You tried different rims rights?

[whyzee125]

Originally Posted by Torgus

I was going to suggest a worn guibo but you didn't stiffen up your diff mounts at all and I wouldn't think the subframe could effect that much...but the diff mounts are in the subframe. Maybe the stock rubber subframe inserts hid it? I'm just throwing out an ideas as that video is loud AF.

Did you say it changes for the worse based on RPM or speed again?

You tried different rims rights?

Guibo is brand new too, but the old one actually looked really good. Diff mounts are new OEM and were replaced with the diff a few years back.

It changes with speed but not RPM. Also doesn't change on or off load or turning, it's always consistent just gets more frequent and louder with speed.

I haven't changed rims, only tires. Both sets roll smoothly and were road force balanced, I just went from Michilen PS to Conti DWS.

[jzx_andy]

Honestly man this sounds like something to do with the driveshaft, diff or bearings. The fact that the noise changes with speeds is also indicative of this, but not entirely conclusive.

If you have ruled every possible culprit out I would say the bushings have a design flaw. This noise is definitely not normal.