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      10-19-2016, 02:09 PM   #1
supernova1
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Cabin noise reduction - simple steps

I want to share results of my experiments with decreasing cabin noise for my 2013 X3 xDrive 28i. I wanted to avoid costly and complex procedures applying extra sound proofing onto entire car body reported numerous times in this forum. Instead, I tried looking for simple, cheap and efficient steps to reduce cabin noise level to a reasonable minimum.

General observation before I started this effort - X3 is relatively quiet car in terms of road and wheel noise – may be because I use Continental Pure Contact tires instead of stock RFTs. My biggest issue with cabin noise stemmed from high frequency noise that fills up the cabin as speed increases. This noise does not seem to have particular dominant frequency and is perceived as high frequency hum echoed inside the spacious cabin. I also saw no correlation of this noise level and the wind speed, and found no to very little effect of the moon roof window as well (experimenting with the moon roof shade). Side mirrors do not contribute to it. It is weakly related to the road noise, judging by the only slight noise change when car drives on different road surfaces or puddles. Noise does modulate well with the car speed.

Here are my steps:

1. Very careful cleaning of all window and door rubber trims/gaskets. I used Meguiar’s Professional rubber and vinyl cleaner, but imagine that there are other suitable cleaners. I paid special attention to cleaning inside the trim window channels, and inside channel pieces where window top edges jam into – they rely on very clean surface to provide air-tight seal. Those particular places were very dirty; I had to clean them several times. I also cleaned all molding mating surfaces of the car body, including bottom plastic trims. I checked the gasket/window alignment, and found no issue. Result – some noise decrease, especially from pass-by cars due to real air tight seal of the window and door.

2. Central pillars have very thin inside plastic panels providing no sound insulation. Tap on them – they sound like a drum, plus left top one sits right next to driver’s left ear. I gently removed those panels (top and bottom pieces) and found that the body pillar top area had a vertical set of ¼” holes, and one 1” hole. They are probably needed to allow air to escape during car body priming dip and for rear door hinge attachment. Pillar itself had no insulation inside, although the outer pillar surface seems to have a secondary sheet metal plate inside. I simply applied small square patches of Dynamat on top of each hole to seal them out. Result – slight decrease of the high frequency hum originated from the pillars; Now, the bottom of each pillar had a large opening for the belt tension mechanism, and this hole opens directly to the outside sheet metal sandwich. There is not much space left around the belt mechanism to apply any sound proofing - ideally I should have removed it, but repair manual suggested replacing the bolt after that – not a route I wanted to follow. Instead, I applied patches of self-adhesive 10mm-thick rubber mat (closed cell, aluminum foil lined) on the back of the bottom plastic pillar cover. It has a set of horizontal ribs that divide the surface into “compartments”. I carefully applied the mat pieces in those “compartments”, leaving just the bottom one empty – this is where car wires pass by. I did not modify the top pillar cover – it is too close to the side air bag. Result – substantial decrease of cabin hum.

3. I did not like how intrusive was the circulation air fan noise – perceived as air swishing. It was quite tiring and emitted directly into my face from the central air vents. So I removed the blower motor from its enclosure (procedure is described elsewhere), being careful not to damage the squirrel cage fan. The fan stayed on the motor shaft – I saw no easy way to remove it. I found that the fan motor main shaft was quite rusty. Although it was spinning freely, I cleaned the fan top bushing with throttle cleaner (being careful not to spray it on the plastic parts), and applied several drops of non-detergent Zoom Spout Oil to the top and bottom bushings (I know that there are several school of thoughts as to what oil to use there), and blew graphite brush dust off with compressed air. I also found that squirrel cage fan was made of awful plastic, and had many surface imperfections on it. I used a piece of 800 grip sand paper and very gently sanded the fan outside blade surfaces, checking that I removed all the imperfections to some degree, and then wiped the dust off with vinyl cleaner. Result – I still hear the fan noise, but it diminished greatly and it does not bother me as it did before. It feels like my fan modifications removed particular frequencies from the blower hum.

4. Rear hatch directional noise. Surprisingly, BMW designed the rear hatch stop light access plates (made of thin plastic) so, that they open directly to the rear stop lights made of thin plastic as well, and there is no sound proofing in those areas at all. I applied patches of Dynamat on the access hatch covers (back side obviously), and added a patch of light-weight rubber foam sheet sound insulation between each cover and the lights, leaving enough space to have access to the light bulb sockets. I tried to be conservative in applying sound proofing there, as motorized hatch does not need extra weight, otherwise it won’t open properly. Result – this was one of the most detrimental changes affecting the cabin directional noise level.

To sum up, procedure #1 is a freebie – it is a commons sense to keep car door and window rubber gaskets clean and conditioned;

Procedure #2 decreased noise a lot – the central pillar belt mechanism opening passes the outer sheet metal vibrations in the cabin easily. The opening is located very close to road to pick up road noise. Plus seam between front and rear door edges in that area has no rubber gasket, allowing wind/road noise to come to the central pillar surface;

Procedure #3 decreased blower fan noise a lot and it is no longer “harsh” – now I just do not notice it;

Procedure #4 was quite simple and effective to remove directional noise that came from back of the car.

My car cabin is much quieter now – but do not ask me about dB numbers! It is simply less tiring when I coast on the highway. Although residual hum is still there (window glass?) – I hope to get to the bottom of it one day and post updates. Side effect is that I can hear more engine noise when car accelerates – but this is one of the joys of owing a BWM!

Hope this write up will help those who are as sensitive to the car cabin hum as I am.
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      10-19-2016, 08:10 PM   #2
mge92
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Do you have instructions and images? / maybe meet up to help me do it to mine?
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      10-20-2016, 01:44 AM   #3
Tjalle
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Impressive work. Congrats!

Since I could only hear engine sound - no exhaust sound -I did it the other way around.
I installed M Performance two-way exhaust system with flaps for Sport and Track modes.

Now I have no problem with any noise above my exhaust sound
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      10-20-2016, 05:12 AM   #4
ninoo
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Thanks Supernova for this interesting and detailed post. this is an area that I also feel needs to be improved . I will carry out at least two of your recommendations today ( window and door seal cleaning and rear hatch mods) and report my findings. I am very happy with my X3 LCI otherwise..

Note. I intend fit NRF Tires at next tire change.
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      10-20-2016, 12:17 PM   #5
ninoo
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Today I cleaned window seals as you described and added some insulating foam and tape around the hatch brake light fitting. I also opened the hatch tail light interior covers to find skimpy patches of sound insulation . I added insulation here also. I am just back from a 100 mile drive and I must say that the back of the car seems quieter.I know that this perception can be affected by hope and expectation.
It would be interesting if someone on this board who has access to a Sound Level Meter was prepared to carry out before and after measurements on the same road in similar weather etc.
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      10-25-2016, 10:02 PM   #6
malicem3
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This is extremely helpful. Putting this on the to-do list.
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      10-27-2016, 08:49 PM   #7
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subscribed. thx op!
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      04-21-2018, 05:45 AM   #8
CKau
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I drove an xDrive30d LCI to see what the road noise and performance was like. I was impressed by how quiet the car was, but I bought a used pre-LCI xDrive30d.

I couldn't believe how much noisier the 2013 F25 is compared to the LCI. So I used the tips in this thread.

I applied Dynamat over the tail lights and on the inside trim used to access the tail lights. There was no insulation whatsoever (compared to Ninoo whose LCI has skimpy insulation).

I also removed the C-pillar trim and applied dynamat to some holes. This is easy to remove. Open the hatch on the side of the boot area and undo the screw. Pull off the trim & you're done.

It was like night & day! This made a huge difference. No need for a sound meter as there is a clear improvement.

I took a slightly different approach with the B- pillar and put Dynamat only over the holes - including the gaping one at the bottom where the belt mechanism comes out. I didn't want to put too much added weight in the car. I also put some foam in there.... marginal result.

I will try applying Dynamat another time to the entire B pillar trim to see what happens, but I'm very happy with the result so far.
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      04-25-2018, 08:28 PM   #9
vestaviascott
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Thanks for the write-up!

I'm definitely going to add this to my to-do list. Great share!
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      04-30-2018, 10:01 AM   #10
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Roughly how much Dynamat is needed? I see a number of different kits available. Is 10 square feet enough?
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      05-03-2018, 10:44 AM   #11
marc x
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Simple my a$$
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      Today, 03:04 AM   #12
CKau
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Update: I use a self adhesive D shaped foam extrusion and stuck it on the front edge of both rear doors. The purpose was to close the gap between the front and rear door on the lower half of the door. The upper half is already sealed by BMW.

HUGE difference!

If someone can point me to a site where I can store photos to link to here, I'd be happy to share photos.

Then the next day I applied self adhesive audio foam, rather than dynamat, to the inside of the B-Pillar and eliminated the remainder of the noise.

What road noise that was remaining sounded like it came from the rear. So I applied the audio foam to that tinny plastic cubby in the boot floor that's on the rear right of the boot (trunk in US English).... the road noise has practically gone!

So the car is now as quiet as my parent's Skoda Octavia which is an awesome result... not quite as whisper quiet as a Golf Mk6 or Mk7.

I suspect if I did the B-Pillar for my F30 328i I would have been happy to keep the car. I got rid of it because it was so noisy... the F25 X3 is already much quieter than the F30 3 series out of the box.
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      Today, 04:47 AM   #13
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Quote:
Originally Posted by CKau View Post
If someone can point me to a site where I can store photos to link to here, I'd be happy to share photos.
https://postimages.org
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