[HighMile335i]

(EDIT: Resolution posted further down!)

Hi All,

Not about my 335i, but about my N54 5 series. Figured I can ask here, as the N54 knowledge runs deep.

My issue is what sounds like a belt squeal at high rpm. Only happens under load--doesn't occur when briefly revved to redline in neutral. It starts squealing around 5k and gets louder and louder.

The weird part is that I replaced the belt/idler/tensioner/tensioner pulley in August, and the squeal continues. Think it might be my alternator/AC compressor/PWS pump? I'm hoping not... they're all pretty costly. That said, because it only happens under load, I worry about the turbos. They only have 30k miles on them though.

Took my mom for a ride the other day and she thought it was tire squeal--it's that loud. Sadly my stock 535xit6 won't break loose... at least not yet!

Hoping to figure it out before it throws the belt and screws up the motor. Thanks!

Link for video (two revs in neutral, then a pull in 1st):

[Dave92N54]

That 100000% sounds like fighting for traction

[HighMile335i]

Originally Posted by Dave92N54

That 100000% sounds like fighting for traction

The belt fighting for traction, do you mean? I'm thinking one of the accessories might have more resistance than it should, or maybe one of the pulleys is upset.

Side note: just installed a new light control module this evening, taking to BMW of Bridgeport tomorrow for coding. The running lamps were staying lit whenever the car is off, so I figured a new LCM would fix. The fronts now turn off, but the rears still stay on when the car is off and locked... bummer for spending $600 on the module, which still requires coding. Hoping BMW can reset something, but otherwise probably another large bill for nothing.

[Dave92N54]

Originally Posted by HighMile335i

The belt fighting for traction, do you mean? I'm thinking one of the accessories might have more resistance than it should, or maybe one of the pulleys is upset.

No I mean tires. That's the only thing I could think of making that kind of sound. It sounds exactly like tires. Does it make that sound in let's say 4th?

[HighMile335i]

Originally Posted by Dave92N54

No I mean tires. That's the only thing I could think of making that kind of sound. It sounds exactly like tires. Does it make that sound in let's say 4th?

It's certainly loud enough to be tires. But it's an xDrive on a stock tune... also has pretty sticky 255s in the back (225s in the front, which isn't ideal, but will replace the wheels/tires in the spring most likely), so I wouldn't think it should so that. It does it in 2nd as well... possibly third, but I can't remember off the top of my head. Don't think I've had it at above 5k RPM in 4th yet, so I'm not sure. I'm worried about throwing the belt, so when it starts to squeal I usually let off.

[Dave92N54]

Originally Posted by HighMile335i

It's certainly loud enough to be tires. But it's an xDrive on a stock tune... also has pretty sticky 255s in the back (225s in the front, which isn't ideal, but will replace the wheels/tires in the spring most likely), so I wouldn't think it should so that. It does it in 2nd as well... possibly third, but I can't remember off the top of my head. Don't think I've had it at above 5k RPM in 4th yet, so I'm not sure. I'm worried about throwing the belt, so when it starts to squeal I usually let off.

Hmm yeah i'm not too sure then. Unfortunately that's all I can make out of the sound, it just sounds exactly like wheel spin to me

[HighMile335i]

Originally Posted by Dave92N54

Hmm yeah i'm not too sure then. Unfortunately that's all I can make out of the sound, it just sounds exactly like wheel spin to me

The more I listen to it, the more I agree with you. Maybe I can find someone local to CT who will let me swap wheels/tires briefly to test! If I was back in Maine I'd just throw the snow tires on and see what happens.

[Bimmer_Bro]

Originally Posted by HighMile335i

Hi All,

Not about my 335i, but about my N54 5 series. Figured I can ask here, as the N54 knowledge runs deep.

My issue is what sounds like a belt squeal at high rpm. Only happens under load--doesn't occur when briefly revved to redline in neutral. It starts squealing around 5k and gets louder and louder.

The weird part is that I replaced the belt/idler/tensioner/tensioner pulley in August, and the squeal continues. Think it might be my alternator/AC compressor/PWS pump? I'm hoping not... they're all pretty costly. That said, because it only happens under load, I worry about the turbos. They only have 30k miles on them though.

Took my mom for a ride the other day and she thought it was tire squeal--it's that loud. Sadly my stock 535xit6 won't break loose... at least not yet!

Hoping to figure it out before it throws the belt and screws up the motor. Thanks!

Link for video (two revs in neutral, then a pull in 1st):

Just have a buddy stand outside the car when you take off. To see if it sounds like the engine area or possible drivetrain?
I have a xi stage 2+ and I can't spin the tires in the dry so I highly doubt it's that.
On a side note, whats the full tire size you running front and rear ?

[HighMile335i]

Originally Posted by Bimmer_Bro

Just have a buddy stand outside the car when you take off. To see if it sounds like the engine area or possible drivetrain?
I have a xi stage 2+ and I can't spin the tires in the dry so I highly doubt it's that.
On a side note, whats the full tire size you running front and rear ?

It's got 225/45/17s on the front and 255/40(?)/17s on the rear. Don't remember if that 40 spec is right for the rear (could be 35), but I previously calculated it and it is within the 1% rolling circumference parameter. That said, I'd rather have a squared setup anyway, so will likely be getting a different set for next spring.

Yes--definitely not breaking loose with xdrive, so it's really perplexing. I hope the AWD is working properly.

I'll try to have someone else listen from outside when I get the car back from the dealership. Replaced the light control module yesterday, started it up and idled for a bit, then shut it down. Had it towed to the dealer for LCM programming, but for some reason it wouldn't start this morning when the tow truck arrived... fired briefly, but then died immediately and would only crank. Glad I hadn't planned on driving it there!

[HighMile335i]

Originally Posted by Dave92N54

No I mean tires. That's the only thing I could think of making that kind of sound. It sounds exactly like tires. Does it make that sound in let's say 4th?

Finally got the car back from the dealership after the biggest bill I’ve paid for any of the 7 BMWs I’ve had.

On my drive to Maine yesterday I put it in 4th and floored it—the screech is still there, which makes me think it’s not tires unfortunately.

I’m now thinking something might be wrong with the PCV system, but it’s hard to believe it would be that loud. Really hoping I don’t need to replace the valve cover, and would hate to do it if it isn’t the cause of the noise.

[HighMile335i]

UPDATE:

Months later, I've got the snow tires on and the squeal is still there. Worse with the stage 1 MHD tune.

I'm thinking it's got to either be a boost leak, or possibly an exhaust leak? The car had new turbos 40k miles ago, so maybe one of the inlets is leaking or something? The MHD data logs show that the boost is taking a bit longer to build than it should, although it eventually reaches the pressure goals. Mostly I'm worried about the turbos over-spinning (if there is indeed a boost leak). Will update as I figure it out when I'm home on break, but would love any suggestions!

[Alkapwn]

In my opinion, granted things sometimes sound different in recording that in person, it doesn't sound like a belt chriping/squealing. And after a considerable amount of this (if it was the belt) you should be able to see wear on it.

Kind of does sound like tire squeal, but it sounds like we've ruled that out. My next guess would be a whistling of some kind, which is likely boost related (maybe vaccum). As it doesn't seem to be present at idle, it may only be leaking under high boost, however I wouldn't entirely rule out a smoke test from being useful. Otherwise,I believe there is a way to command boost "manually" so as to replicate the issue while stationary. However that's a little sketchy. Maybe a few gopros under the hood while drivng can help pinpoint the trouble area further.

Or maybe vacuum theory (something that's connected to the vacuum pump) may be easier to disprove first.

[HighMile335i]

Originally Posted by Alkapwn

My next guess would be a whistling of some kind, which is likely boost related (maybe vaccum). As it doesn't seem to be present at idle, it may only be leaking under high boost, however I wouldn't entirely rule out a smoke test from being useful. Otherwise,I believe there is a way to command boost "manually" so as to replicate the issue while stationary. However that's a little sketchy. Maybe a few gopros under the hood while drivng can help pinpoint the trouble area further.

Or maybe vacuum theory (something that's connected to the vacuum pump) may be easier to disprove first.

Yes--I'm thinking it must be a boost leak or something vacuum-related. I've rigged up a fitting to pressure-test the boost system with my compressor (last time I discovered the diverter valves were leaking), so I'll try it again. I should be able to pressurize the system up to 20psi, but because the screech happened at stock boost levels I'd imagine it would take much less than that. However, the fitting I made attaches to the hot side of the intercooler, so theoretically there could be a leak from the turbos that I wouldn't see. Will cross that bridge if necessary.

The GoPro suggestion is a good idea... I can mount it in a few different spots to try to pinpoint where the sound is coming from. In a few weeks I'll have some time for further diagnosis and will post an update.

[HighMile335i]

Hi All,

Finally I can post a resolution (sort of) to this thread! Really irks me when I find a thread that describes my issue, but there's no resolution–I won't leave y'all hanging!

A few months ago, I started to think that I may have an exhaust leak that was causing the noise in the video. Right after that, I noticed an exhaust-leak-type of sound. I stumbled across a thread on another forum posted by an X5 owner who had a similar noise, and it turned out to be a leaking turbo manifold gasket.

Long story short, I removed my expansion tank and boost control solenoid mounting panel, and over 2/3 of the turbo manifold nuts were super loose! Insane... I can only assume that the shop that replaced the turbos 50k miles ago reused the copper nuts rather than replacing them, and thus they loosened over time.

Luckily, the E61 engine bay is large enough that I can reach my hand down and tighten most of the nuts from the top. It's a tight fit and I wasn't able to reach the very bottom ones, but went for a drive and the noise was different (quieter), so tightening the nuts had an effect. I'm going to order all new hardware and try to replace all the nuts from the top–will be tricky, but not as tricky as pulling the turbos and going from the bottom!