Grinding Noise
 

So I’ve been dealing with an annoying grinding or vibration noise coming from somewhere in the drivetrain. I‘ve got the A8 transmission. Multiple service departments have been “unable to reproduce” the issue, but one went ahead and did the transmission flush for me anyway. I don’t think it’s the usual shudder…it’s definitely a sound and not a feeling while I’ve heard the shudder is more of a sensation in the steering wheel. It’s worst up hill and always during acceleration. At first I thought it was during gear changes but I threw it into manual mode and it still happened. I was finally able to get some audio of it, it’s not as good as being there live but you can definitely hear it when it happens. I even added some cues to make it easier to spot. 😄

Anyone familiar with this mystery sound?

https://youtube.com/shorts/1qSbB85HwkA?feature=share

This sounds much more like gear grinding than rumble strips, I'm also leaning towards this being a different issue.

It's the first time I'm hearing this specific noise, so I don't think I can help, hopefully someone with more experience will :noidea:

That would annoy the heck out of me….Just from the video, it sounds like a low rpm on throttle metal on metal vibration. Possibly the exhaust rubbing, maybe something else (although kinda hard to tell not being there) Do you have NPP? If so, I’d pulling the NPP fuse to deactivate a possibly noisy valve. If that doesn’t quiet it down, I’d be checking the rest of the exhaust and heat shields.

Good luck, mystery noises can be a PIA.

It’s annoying alright! And more than a little embarrassing to take off from a stoplight and have it grind like that…sounds like I don’t know how to drive a stick (though it’s actually an automatic.) Definitely sounds like metal on metal but there’s no felt vibration anywhere. Not the steering wheel, shifter, or in the seat.

I don’t have NPP.

Does yours have cylinder deactivation? If so, it could also be one of the AFM valves needing to be lubricated. Just throwing things out there…

Grinding Noise
 

It does have the AFM…I read somewhere that that might cause a noise.

I also wonder about hill start assist, if the clutch may have an issue or something since it always seems to get worse uphill.


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I also favor this theory. AFM is in that ballpark.
This sounds like you are hitting a resonance frequency and something is vibrating.

Thank you both, I will take a look for something loose.


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