[Helant1]

Having changed to a 2010 325i from my beloved 2003 525i, I was disappointed by how much noisier it was. On searching the forums I found a promising post from CKau (http://f30.bimmerpost.com/forums/sho...d.php?t=757485), which told about covering holes in the wheel arch and which made a "substantial reduction" in noise level.

I thought it would be good to try and quantify how much difference this made, so downloaded a sound meter app to my phone and measured 'before and after'.

On looking in the engine bay, I also found the three holes in the wheel arch. eBay provided a sample size piece of sticky backed sound insulation foam, and it was an easy task to cover the holes.

Nearby was a stretch of road with relatively new but coarse tarmac. I did a mile run each way with the cruise control set to 54mph, and took the average noise level from the sound meter app (fan and aircon turned off!).

Noise level with holes uncovered: 74.5 dB
Noise level with holes covered: 71 dB

An amazing 3.5 dB difference, or in other words - noise reduced by just over half!

If you've got an e90 or e91, recommend you look in the engine bay for these holes, and if they're there - cover them!

Amazing and frustrating that BMW didn't bother to do this at time of manufacture!

[gunnerxq]

Originally Posted by Helant1

Having changed to a 2010 325i from my beloved 2003 525i, I was disappointed by how much noisier it was. On searching the forums I found a promising post from CKau (http://f30.bimmerpost.com/forums/sho...d.php?t=757485), which told about covering holes in the wheel arch and which made a "substantial reduction" in noise level.

I thought it would be good to try and quantify how much difference this made, so downloaded a sound meter app to my phone and measured 'before and after'.

On looking in the engine bay, I also found the three holes in the wheel arch. eBay provided a sample size piece of sticky backed sound insulation foam, and it was an easy task to cover the holes.

Nearby was a stretch of road with relatively new but coarse tarmac. I did a mile run each way with the cruise control set to 54mph, and took the average noise level from the sound meter app (fan and aircon turned off!).

Noise level with holes uncovered: 74.5 dB
Noise level with holes covered: 71 dB

An amazing 3.5 dB difference, or in other words - noise reduced by just over half!

If you've got an e90 or e91, recommend you look in the engine bay for these holes, and if they're there - cover them!

Amazing and frustrating that BMW didn't bother to do this at time of manufacture!

I can't see the pictures.

Photobucket is such a pisser

OP: any other pics of what you're talking about?

[Andy198712]

i saw those holes a while ago, and thought i was missing a part of trim in the engine bay! so you just used some sound deadening foam? got a link?

[gunnerxq]

Originally Posted by Andy198712

i saw those holes a while ago, and thought i was missing a part of trim in the engine bay! so you just used some sound deadening foam? got a link?

What holes? I can't see any pictures

[Digitalize]

The holes are for mounting an auxiliary water pump, not all cars/regions had them.

I'm personally not convinced covering them would make that much noticeable change, as it's only open in to the engine bay, which is still separated from the cabin.

[DrRobert]

And FYI most of those dB meter cell phone apps are notoriously inaccurate.

[The Nightman]

This thread piqued my interest so I took a look around my engine bay and found the holes in question. They are located on the LHS strut tower, below the PS reservoir on my Canadian 2009 E90 328i:





Any suggestions on what material to use to cover them?

[juld0zer]

Flashing? I'm not sure if engine bay heat is comparable to summer rooftop heat though

[The Nightman]

You can get better access to these holes from the wheel well with the wheel removed:



There's also a larger hole in front of the three holes so I'm skeptical that covering the three holes will make a difference. Seems simple enough to slap some flashing over it next time you're in there though.

[The Nightman]

So I had a go at this. I used poor man's Dynamat leftover from another project. It's basically 40mil bitumen flashing (http://www.resisto.ca/product/multip...fing-membrane/), similar to Peel & Seal in the US. Probably not the ideal material for this but it's what I had on hand. I covered the holes up from the wheel well side.


Here are the three holes for the auxiliary water pump.


Here is the larger hole for the brake hard line and wiring for the brake pad sensor.


I used cardboard to make a template with rough measurements. I used two pieces to accommodate the brake line.



Bitumen flashing applied.



This is the RHS wheel well. There is only the large hole with a corrugated tube coming out, making it difficult to cover. There is already a heat shield on the engine bay side covering the hole. I don't think there's much room for improvement here.

I'll post an update after some seat time and report whether or not this made any difference. I'm skeptical since the holes go into the engine bay, but this project is easy enough to experiment with.

Update:
I went for a drive and I'm quite shocked at the difference in road noise. I didn't take any measurements but there is definitely a reduction in road noise from the front of the car. It's not a significant decrease but road noise is less intrusive compared to before. This is after 20 min of city driving and 20 min of highway driving at speeds of 100-130 kph.

For the minimal cost and effort to seal the holes in the wheel well, I highly recommend giving it a try.

[slupie]

Also check if all of your lift blocks are in place (4X). On E91 if the sunroof panels are miss-adjusted then the wind noise is is very loud. Leading ledge of each panel needs to be lower than the trailing edges. My panoramic roof was adjusted twice at the dealer before the wind noise was almost eliminated.

[tlow98]

Interesting post! Considering the wheel well is the loudest part of a moving car this would make sense.

On the e91 there is an updated pano roof seal. It's the same as the x3 of that generation. Part was updated and cuts down on wind noise a lot.

[McPikie]

Originally Posted by tlow98

Interesting post! Considering the wheel well is the loudest part of a moving car this would make sense.

On the e91 there is an updated pano roof seal. It's the same as the x3 of that generation. Part was updated and cuts down on wind noise a lot.

Any more info on this as the noise from my pan roof is horrific

[tlow98]

Originally Posted by McPikie

Any more info on this as the noise from my pan roof is horrific

You can find the updated part number on realoem.com. Iirc, was like $50

[The Nightman]

Originally Posted by freedomfries

I'll post an update after some seat time and report whether or not this made any difference. I'm quite skeptical since the holes go into the engine bay, but this project is easy enough to experiment with.

I went for a drive and I'm quite shocked at the difference in road noise. I didn't take any measurements but there is definitely a reduction in road noise from the front of the car. It's not a significant decrease but road noise is less intrusive compared to before. This is after 20 min of city driving and 20 min of highway driving at speeds of 100-130 kph.

For the minimal cost and effort to seal the holes in the wheel well, I highly recommend giving it a try.

[Blueeyesredpanda]

Originally Posted by freedomfries

I went for a drive and I'm quite shocked at the difference in road noise. I didn't take any measurements but there is definitely a reduction in road noise from the front of the car. It's not a significant decrease but road noise is less intrusive compared to before. This is after 20 min of city driving and 20 min of highway driving at speeds of 100-130 kph.

For the minimal cost and effort to seal the holes in the wheel well, I highly recommend giving it a try.

How's it holding up? Any rust? (Hint: your trunk)

[Tambohamilton]

Why would covering holes in the front wheel arches make the trunk rust?? Or have I misread your post...?

[Tambohamilton]

Just looked under my bonnet (hood, for you Americans ), and my car has plastic covers clipped into the openings around the brake lines, and the aux water pump mounts go a decent way towards filling in those 3 holes with rubber... I think there should be factory fit parts for this, rather than gluing stuff over the holes. Not that I've got a problem with cheap fixes, but it's surely much less hassle to just clip in a bit of plastic if it's available.

[Serf27]

Originally Posted by tlow98

Interesting post! Considering the wheel well is the loudest part of a moving car this would make sense.

On the e91 there is an updated pano roof seal. It's the same as the x3 of that generation. Part was updated and cuts down on wind noise a lot.

Is this the seal to reduce wind noise with the pano cover open and the glass closed?!

I like driving with the cover open but the wind noise always forces me to shut up.

[tlow98]

Originally Posted by Serf27

Is this the seal to reduce wind noise with the pano cover open and the glass closed?!

I like driving with the cover open but the wind noise always forces me to shut up.

Yes, Bmw revised the design of the seal. If you replace this there is zero difference in noise with the cover open or closed. There is a good thread about the procedure floating around. Took me about an hour.

Wish I had done it sooner!

[Serf27]

Originally Posted by tlow98

Yes, Bmw revised the design of the seal. If you replace this there is zero difference in noise with the cover open or closed. There is a good thread about the procedure floating around. Took me about an hour.

Wish I had done it sooner!

Thank you!

I always thought that was just one of those things you had to live with.