I have a 2001 Audi A4 1.8t awd automatic with 100k miles. When I release the accelerator and coast, there is a knocking noise coming from the rear that I hear for 3 seconds. It is not very loud, but has been getting worse. It sounds like it is on the right side, but it is difficult to tell for sure. I checked the suspension components and everything looks OK. The boots for the CVs look fine. The noise occurs in drive and in neutral. It stops more quickly when brakes are applied and I believe this is because the car decelerates more quickly.

Does anyone have any ideas on what this could be? I am thinking that there may be an issue with the rear differential. I am going to drain it and check the fluid for metal, but any other ideas?

 

Most common A4 driveline noise around 100K miles is due to a bad wheel bearing.

 

diff mount, trans mount, subframe mounts, something like that. Maybe driveshaft. Doesn't sound like a wheel bearing to me.

 

Greed - I'm thinking driveshaft balance or u-joint, or maybe one of the mounts.

 

I'll chime in with a possible u-joint problem

 

Thinking about it, I had a blowout on that right side tire shortly before this started happening. I don't know if it could be related...

 

Thinking rear CV.. think about it and you'll see why.

 

well, I have a 2002 audi s4, auto awd. There is a low "growl" coming from the rightish rear area of the car. I am replacing the cv boots this weekend, had a few problems near the end of the 4.5k km trip. This noise started around the 600km mark. I too looked at all the components of the suspension and brakes and everything seemed ok. noise starts at around 20-30 km, but you can only hear it if the cd player and heating (fans) are off, more noticable around 40-50kmph. Its like a low drone noise. Parts guy thought maybe wheel bearing. Someone suggested unbalanced driveshaft, but from experience with my 94 90CS, was much different.

 

Fliparto, does it get louder in a left turn? If so, and it seems so anyway, it's very likely a wheel bearing. They're common and not terrible to change. I pull the hub off and take it to a shop to have the old bearing pressed out and the new one pressed in. I get my bearing kits from www.germanautoparts.com for $56 shipped (bearing and end axle bolt).

 

No noise difference no matter what i do except vehicle speed