Help - Cabin humming noise

[bluecan]

Looking for some input before bring it to the shop.
09 A4 123k miles Quattro 2.0T.
Have this noise for a couple months and can not figure out where the noise come from. I posted a link to the YouTube video.
https://youtu.be/j1Np1GI-6Jc
This noise started when the car speed hits 15 mph and gets louder as the speed increase. No code pops up. Doesn’t affect the drivability. The noise can basically only heard inside the cabin. With the windows rolled down, it can’t be heard from outside or it doesn’t get louder. Had someone standing on the street and the car drove by, no obvious noises heard.
Put the car in P, rev the engine, no noise. It only appears during driving. Turning doesn’t make it worse or better.
Put the car to N at speed 40mph, the noise is there. I even shut off the engine and let it rolls, it is still there.

Any input is greatly appreciated!


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[mtroxel]

So you could turn off the motor at 40mph and you'd have that noise?

I'm betting center bearing on the drive shaft. They can be hard to see when they're installed. I had to remove the shaft from my old B5.5 to see what was going on here.

[bluecan]

So you could turn off the motor at 40mph and you'd have that noise?

I'm betting center bearing on the drive shaft. They can be hard to see when they're installed. I had to remove the shaft from my old B5.5 to see what was going on here.

Yes, shifted to N and turned off engine, got the same noise as if the engine is on. No difference.

Do you know there is anyway I can test that center bearing? Thanks.


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[mtroxel]

Do you know there is anyway I can test that center bearing? Thanks.


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I you pull off the heat shield and exhaust so you get to it, you can put a bright light behind it while you grab the shaft and flex it around. If its torn like the one above...or even just really thin in spots, you should see light coming through the rubber.

[bluecan]

I you pull off the heat shield and exhaust so you get to it, you can put a bright light behind it while you grab the shaft and flex it around. If its torn like the one above...or even just really thin in spots, you should see light coming through the rubber.

Thanks! Will check it out.


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[slowpokeB8]

@mtroxel - Did you experience any driveline vibration with this bearing being worn out? I currently have a very noticeable driveline vibration in my allroad and it's worse in higher torque situations. It definitely feels like it could be a driveshaft issue.

[mtroxel]

@mtroxel - Did you experience any driveline vibration with this bearing being worn out?

Yea I did. That was years ago but as I recall mine came on at about 40 mph, and particularly when I'd let off the gas - not accelerating or decelerating. It made a little noise, but mostly it was a vibration right under between the seats. But I've read about these enough around here to know that the symptoms can vary.

[findalex]

if you do a search for propeller shaft issues w/ Porsche or VW SUV's, you'll find that it is a common problem for the rubber to disintegrate. It was so common, but so expensive to fix "the corrrect" way because you have to change out the entire shaft, that some after market solutions have come out. The funniest DIY solutions seems to be cutting up pieces of rubber tubes to put in place of the rubber, but it also seemed to work.

humming could also be caused by the tire wearing incorrectly (cupping) due to bad suspension components. if there's no vibration and just noise, check to see if the noise goes away after you get new tires.

[S-Liner]

I say wheel bearing(s), I mean it’s an ‘09 w/123K miles


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[Theiceman]

maybe it just doesnt know the words ?

[bluecan]

Had the car on jack stand today. It appear the noise is not from the central bearing. The shaft feels pretty solid offline. https://youtube.com/shorts/oaimDSrHe0o?feature=share

The abs brake light came up and with the car up on jacks.


What could be the next suspect?
The weird thing is it is very loud inside the cabin and not getting louder with the windows rolled down.

Getting a stethoscope.


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[bluecan]

I say wheel bearing(s), I mean it’s an ‘09 w/123K miles


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Replaced the left side wheel bearing a few weeks ago when I thought the noise came from it. Getting a stethoscope to listen type right side. Hopefully make diagnosis easier.


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[mtroxel]

That's a tough one. I listened to your first vid again. The frequency is almost too high to sound like a center bearing. But its loud enough I'm sure you'd hear it with a stethoscope on a wheel bearing...might even hear it just turning the wheel by hand.

I don't hear it at all in the second vid you just posted today. Was the spedo reading over 15 mph in that second vid? Or maybe something needs to be under some kind of load to reproduce the noise...

[S-Liner]

Those wheel bearings are a pain in the ass to diagnose properly. I just changed out the right rear believing it was at fault, it turns out my left is shot.

The in-cabin acoustics make it difficult because the sound seems to be coming from all four corners so a stethoscope would be the ideal method to pinpoint the issue.


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[RPMtech147]

Those wheel bearings are a pain in the ass to diagnose properly. I just changed out the right rear believing it was at fault, it turns out my left is shot.

The in-cabin acoustics make it difficult because the sound seems to be coming from all four corners so a stethoscope would be the ideal method to pinpoint the issue.


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+ 4 jackstands. You will need a helper. Warning, if you do it wrong, you'll die.

I do it all the time but using a lift. Don't go crazy. Just get the wheels moving fast enough to hear the noise and start checking bearings and such.

I also vote bad wheel bearing but it could be center bearing or a bearing in the transmission(center diff), front or or rear diff, etc..but it sounds like a wasted wheel bearing.


If you don't like tempting fate, you need one of these.

or just pay a shop $150 to diagnose it.

[bluecan]

+ 4 jackstands. You will need a helper. Warning, if you do it wrong, you'll die.

I do it all the time but using a lift. Don't go crazy. Just get the wheels moving fast enough to hear the noise and start checking bearings and such.

I also vote bad wheel bearing but it could be center bearing or a bearing in the transmission(center diff), front or or rear diff, etc..but it sounds like a wasted wheel bearing.


If you don't like tempting fate, you need one of these.

or just pay a shop $150 to diagnose it.

Got that stethoscope from Amazon $20.
The passenger side knuckle is much louder while the driver side has a new wheel bearing. Put the stethoscope pin to the transmission hub where connects the cv axle, got the similar noise. The speed was around 25 mph when I tested everything. At this point I can pin point the exact part. If it requires taking off the cv axle, I probably need to bring it to the shop. Thanks for your input.


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[bluecan]

That's a tough one. I listened to your first vid again. The frequency is almost too high to sound like a center bearing. But its loud enough I'm sure you'd hear it with a stethoscope on a wheel bearing...might even hear it just turning the wheel by hand.

I don't hear it at all in the second vid you just posted today. Was the spedo reading over 15 mph in that second vid? Or maybe something needs to be under some kind of load to reproduce the noise...

The car was not at high speed, I put it at m2 and it was around 13 mph. Another weird thing is, I couldn’t reproduce the same noise on the jack stands. The noise is so loud in the cabin and can’t be picked up from outside the car.


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[mtroxel]

Lots of time a wheel bearing will make more noise depending on which way the wheel is turned. When you turn the wheel one way or the other with the wheels rolling on the ground, you load it up.

[bluecan]

Just to update on this. I changed the front passenger wheel bearing and the noise disappeared. The bearing has no play at any direction, it just makes humming noise. Thanks for everyone’s input!!


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[mtroxel]

Bearing noises can be tough to nlocate. Glad you got it.