Very strange noise from the rear of the car
06-13-2015, 11:16 AM
#1
Very strange noise from the rear of the car I have a strange noise I can't figure out that started last night. When I'm driving there's a sort of knocking noise coming from somewhere in the back of the car. Best I can describe it is imagine lightly tapping your knuckles on fiberglass. It's rotational in nature and seems to increase with speed. I can only hear it around 20-30mph. Below 20 or so I can't hear it and faster than 30 or so the exhaust/road noise drowns it out. It doesn't seem to be coming from one side or the other that I can tell. To give you an idea of the sound, my first thought when hearing it was that the hatch was open and bouncing. Car is an '01 WS6 A4 with G80, 100k miles; not raced, only spirited road driving.
It doesn't sound like a bearing to me, as when I've had those wear out in the past they make more of a constant grinding noise, and this is cyclical like "tap tap tap tap". We put the car up on stands this morning, put it in neutral and spun the wheels by hand. There was some grinding noise from the brakes on the right side, so we took it apart and found the e-brake was rubbing. Put it all back together, took it out and the knocking noise is still there; so it's not brakes. Also checked the exhaust and it's not rubbing the driveshaft.
Only things I can thing of at this point are something is hitting the driveshaft or the U joint; but I don't see anything. Or maybe the torque arm mount/bushing? The fact that it's rotational is what's got me, because otherwise I'd suspect something in the suspension.
Thoughts?
It doesn't sound like a bearing to me, as when I've had those wear out in the past they make more of a constant grinding noise, and this is cyclical like "tap tap tap tap". We put the car up on stands this morning, put it in neutral and spun the wheels by hand. There was some grinding noise from the brakes on the right side, so we took it apart and found the e-brake was rubbing. Put it all back together, took it out and the knocking noise is still there; so it's not brakes. Also checked the exhaust and it's not rubbing the driveshaft.
Only things I can thing of at this point are something is hitting the driveshaft or the U joint; but I don't see anything. Or maybe the torque arm mount/bushing? The fact that it's rotational is what's got me, because otherwise I'd suspect something in the suspension.
Thoughts?
06-13-2015, 12:11 PM
#2
If you have the factory torque arm, check to make sure it isn't bending approx six inches from the rear end. They are known to do this, I saw one that came in to the shop that was so bent the rear springs had almost fallen out of the pockets. Bob
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ATI ProCharger and Moser Sales 260 672-2076
PM's disabled, please e-mail me
E-mail: brutespeed@gmail.comob@brutespeed.com
https://brutespeed.com/ Link to website
06-13-2015, 02:03 PM
#3
Figured it out. It was something incredibly stupid. After tearing through the right side this morning we decided after lunch to take apart the left side. Go to take the wheel off and the first 3 lug nuts are like finger loose. Tighten them up and all is good. The wheels were put on with an impact last time and the other three were still tight. All I can guess is some ******* thought he was going to take my wheels and quit when he saw I had locks on them.