Humming noise when driving above 50km/h

[Arese]

Hi everyone, at around 59,800km my 2016 S5 started exhibiting a humming noise in the cabin. It sounds like a sound coming from a rotating motion. The noise is only audible above 50km/h. If I go slow, it will fade away and when I go above 50km/h it comes back and it's always the same sort of noise/humming.
It's really subtle and at first, I thought I was in sports mode with the exhaust in dynamic but it's not the case, when I hear the exhaust I can clearly tell the strange humming sound apart from the sound of the exhaust when accelerating or decelerating. It's something else.
It's also had to pinpoint where it's coming from, I don't think it's coming from the engine bay but it sort of fills the whole cabin like a background noise.

I checked an old dashcam footage from before and I'm now positive that this is not in my head. I've made a quick video using some dashcam footages, it's not as obvious as in person on the video but if you listen closely you can hear the humming sound as I go over and below 50km/h. At the end of the video, I added an old footage from before the issue where I'm doing 60km/h with no humming sound https://youtu.be/q_gn4PqGLCc

It's a long shot but has anyone ever heard/experienced something similar?

The car is due for the 60k gearbox service, could old oil gear be the reason for this humming noise? What about the rear differential?

If you have any ideas please let me know

Thanks

[dbtong]

I can barely hear any humming noise in your video but could it be your tires? Can you see any uneven wear or "scalloping" of the tread? I once had a set of tires that made so much noise I thought it was a bad wheel bearing.

[Arese]

I can barely hear any humming noise in your video but could it be your tires? Can you see any uneven wear or "scalloping" of the tread? I once had a set of tires that made so much noise I thought it was a bad wheel bearing.

Hey Dave thanks for the reply and for taking the time to check my video. Yes that's what I thought, I'm quite sensitive to noises, more than the average person and it was my fear that people wouldn't notice it, it's also less noticeable on the video.

I initially thought about tires as the noise seemed to come from a rotating motion. I checked my tires and no uneven wear.
However, I just thought about something, my rear tires just reached the tire wear indicator and they are also 6 years old. Is that wear indicator made of a different rubber VS the rest of the tire which would explain that different noise/humming I now hear?

The noise does mmmMmmm, at one point there's a higher note, and a the same speed it repeats itself. If I go faster, I can tell the rotation is going faster, for example instead of mmmMmmm, it will become mMm, mMm, mMm... if that makes sense.

Are tires designed to make more noise when they reach the wear indicator?

You mentioned wheel bearings and I came across this video where ChrisFix tries to illustrate what a bad wheel bearing sounds like. It's also subtle in the video but you can hear a background noise. But he does say that it is an obvious sound and that he can pinpoint from which wheel the sound is coming from. In my case I can't it's sort of filling the whole cabin and I can't pinpoint the source.
https://www.youtube.com/watch?v=YvKWGjmPKoc

Thanks

[old guy]

You can try rotating your wheels/tires and see if you experience any change in the noise. I had a similar issue on my B6 years ago. I chased everything imaginable and finally located the source by swapping wheels/tires with another vehicle. The tires were evenly worn, but low on tread depth.

[eskimo0101]

Good chance if you're at the wear bars it's just the worn tires making the noise. I've had plenty of tires that didn't feel/look cupped but made a lot of noise as they got worn out. I'd start with a fresh set of tires since they need to be replaced regardless at this point and see if the noise goes away.

[Arese]

You can try rotating your wheels/tires and see if you experience any change in the noise. I had a similar issue on my B6 years ago. I chased everything imaginable and finally located the source by swapping wheels/tires with another vehicle. The tires were evenly worn, but low on tread depth.

Good chance if you're at the wear bars it's just the worn tires making the noise. I've had plenty of tires that didn't feel/look cupped but made a lot of noise as they got worn out. I'd start with a fresh set of tires since they need to be replaced regardless at this point and see if the noise goes away.

Thanks guys for the input.
Just a quick update, I had a friend ride with me and he was able to hear the humming noise. The way he put it was that it sounds like a spinning washing machine.

Also last time I posted, I only drove the car in the neighborhood driving at 60km/h but recently I noticed that the sound became louder the faster I go, especially when I reach 70km/.

The more I read about wheel bearing failures and the more I think it may be that.

For example, I found a site describing the symptoms of a bad wheel bearing
1. Noise:
- A humming, rumbling or growling noise that increases with acceleration or as the vehicle turns. (This is what I'm describing)
- A loud constant whining or grinding noise when the vehicle is in motion.
- Clunking noises when driving over uneven road surfaces.
2. Looseness, excessive play in the steering wheel (vague steering);
3. Steering wheel vibration which changes with the vehicle speed or as the vehicle turns;
4. ABS malfunctioning. ABS system issues can be related to failure of the ABS sensor that is integrated in the wheel end bearing.

And in the section about why wheel bearings fail, they mention inappropriate use of a hammer that can cause damage to the exterior or interior of the wheel bearing.

I recently replaced my 4 rotors + pads. The 2 factory rear rotors were completely stuck and couldn't take them off using my rubber hammer (that's what I usually use to hit the edge of the rotor to dislodge it) so I used a heavier metal hammer to hit the rear rotors, it worked but I had to really hit hard. Now I'm wondering if I didn't damage my wheel bearings.

I read online that cars with ABS systems built into the wheel bearing would trigger a fault code in VCDS when wheel bearings go bad. Would that be the case with the S5?

But I agree with you 2, I'll start with a set of fresh tires since I have to replace them anyway, if I'm lucky the noise will be gone, if the noise is still there, it will start to look likely that it may be bad wheel bearings.

I'll get new tires next week and keep you guys posted.

[freshjive]

My guess would be wheel bearings. Go on a straight road and do 'S' turns. You should hear the tone of the noise change with steering input.

[Arese]

Quick update, fitted a set of new tires at the rear plus full wheel alignment (Front & Rear) and unfortunately, the noise is still there.

My guess would be wheel bearings. Go on a straight road and do 'S' turns. You should hear the tone of the noise change with steering input.

Ok I haven't tried that, will do tomorrow.
Besides doing S turn, is there any way to visually check for a bad wheel bearing?

I watched a video online and the guys lift the car to rock the wheel left/right and top/bottom, if it moves or loose that points towards a bad wheel bearing. Then he rotates the wheel and if it's not frictionless and makes a rumbling sort of noise it's definitely a bad wheel bearing according to him.
https://www.youtube.com/watch?v=vJYDGWEwhEk
Also in the video he starts with a road test and the sound on the car he's testing is really similar to mine.

Now that I confirmed it's not the tires, everything points to a bad wheel bearing right? What could it be when it's a speed-dependent noise like that?

I'll try doing S turns and jack up the car and rock the wheel and see if the results are conclusive. I never replaced a wheel bearing I have to see if I can do it myself. If anyone got a link to a tutorial or video for an S5 please share.

[freshjive]

The only way to check them is to shake the wheel side to side/ top to bottom. Some times you may have a bad wheel bearing but it doesn't have any play yet.
They aren't hard so long as you have the correct tools. Don't strip the triple square bolt at the back or you're going to have a very bad time. Either cutting the bearing from the knuckle or removing the whole steering knuckle entirely.

[Arese]

The only way to check them is to shake the wheel side to side/ top to bottom. Some times you may have a bad wheel bearing but it doesn't have any play yet.
They aren't hard so long as you have the correct tools. Don't strip the triple square bolt at the back or you're going to have a very bad time. Either cutting the bearing from the knuckle or removing the whole steering knuckle entirely.

So I lifted the car and did the shakedown test and the rear right is definitely bad, it got play and makes a grinding noise when I shake it from top to bottom.
Rear left is not as pronounced but the grinding noise is still present with a little bit of play.
Just to compare I tested the front wheels and it's quite obvious, no play, no noise so I'm fairly confident that this is the issue.

I watched a few videos and it's not a hard job, it's more the execution that is tricky and like you said requires the right tools. It's pretty much a brake job as you have to take off the rotor, then you have to remove those 4 triple square bolts from the back which is the tricky part, and then detach the hub from the wheel bearing, which requires a bearing splitter.
I also don't have a press to press the hub back into the new wheel bearing but I saw a guy using an alternative method. He just used the axle bolt and tightened it and it slowly pushed the hub against the wheel bearing.

I got a quote from a shop and they charge 3h of labor per side + parts for a total of $A1500 which is like $US1000

I'm gonna do it myself, just worried to strip those triple square bolts but other than that it should be fine. I'll try to buy the right extensions and a quality triple square socket to minimize any risk to strip them.

I'm wondering if I shouldn't also replace the wheel hub while I'm at it. That way I can just throw away the old wheel hub/wheel bearing and don't bother trying to detach them. I'm also conscious that I might have damaged the wheel bearing when I hit the rotor with a hammer to take the rotor off and I'm wondering if I didn't damage or bend the wheel hub as well in the process? It's a big job, I'd rather replace everything than risking having to go back in there later

[freshjive]

If i were in your position with no tools, i would just remove the bearing yourself and find a shop to press off the old one and installed the new one. No need to replace the wheel hub. It takes a considerable amount of force to bend a wheel hub. Unless this was a vehicle that you crashed into the curb with and broke suspension components i wouldn't replace it.

What happened to you is just textbook case of cause and effect. Any time i have to remove a rotor from a vehicle i always use a deadblow hammer. Way back in my early days i learned the tough lesson of why you don't use a hammer to remove rotors because the shock that transmits through the knuckle can cause the bearing to fail. Ive seen if first hand to other people. One guy does brakes and the customer comes back a day or two later complaining of a rumbling noise that wasn't there.

[Arese]

If i were in your position with no tools, i would just remove the bearing yourself and find a shop to press off the old one and installed the new one. No need to replace the wheel hub. It takes a considerable amount of force to bend a wheel hub. Unless this was a vehicle that you crashed into the curb with and broke suspension components i wouldn't replace it.

What happened to you is just textbook case of cause and effect. Any time i have to remove a rotor from a vehicle i always use a deadblow hammer. Way back in my early days i learned the tough lesson of why you don't use a hammer to remove rotors because the shock that transmits through the knuckle can cause the bearing to fail. Ive seen if first hand to other people. One guy does brakes and the customer comes back a day or two later complaining of a rumbling noise that wasn't there.

Yes I have been thinking about going to my local mechanic and ask him if he can separate them and press the new one back in for me. I should be able to find someone to do that for me.

Anyway, I started the job this morning. Took off the caliper, caliper carrier, and the protection thing and now have full access to the hub assembly.
I located the 4 triple square bolts.
The 2 bolts at the top are easy to access, but the bottom ones are hard to access, my triple square bits are too long and can't fit in





I'm guessing I need low-profile sockets to fit in there, something like that?
https://www.amazon.com.au/TITAN-1613...004WIWN1U?th=1

I ordered those online and went to my local too shop to buy flex ratchet with the thinnest head I could find


I saw a youtube video where he was able to undo the bottom bolts using this flex ratchet




I don't have the low profile triple square socket yet but I checked with the flex ratchet if I get better access, it's still super tight, the head of the ratchet is blocked by the CV boot rubber and doesn't let me position myself correctly in front of the bolt. I'll try to figure it out tomorrow but unsure it will work. I've seen videos where people don't take out the CV boot to do the job.

Any tip is appreciated

[freshjive]

either find some low profile sockets to fit or remove that collar that is obstructing you. You will need to do a wheel alignment if you remove that collar but it will give you all the room you needs.

[findalex]

I just replied to your other post on audiworld.

https://youtu.be/3TgupkZwvs8

[Arese]

Hi everyone, got the new wheel bearings installed and the humming sound is gone so it was indeed bag bearings.
Thanks to everyone who helped me troubleshoot.

If anyone comes across this thread in the future with a similar sort of issue, check out my other thread for pointers on how to get the job done https://www.audiworld.com/forums/aud...aring-3059418/

Cheers