Help identifying clunk sound from rear suspension *video*

[maccalo]

I've had this strange clunk sound coming from the rear suspension on the right side of the car every now and then when driving over bumps at medium speed. Lately, the sound has become more pronounced.

I have localized its origin to be somewhere near the right rear wheel base. Video:


(sound @ 0.06)

What I have done so far (maintenance, not to eliminate sound)
- New rear shocks
- Replaced sway bar end links
- Replaced sway bar bushings
- Powerflex rear diff mount
- Removed spare wheel and tools to eliminate sources from inside the car

Right rear wheel bearing didn't pass inspection, but I don't think a shot wheel bearing would make such noise?
Any ideas on what to do next?

[diuvic]

Does it only sound like that when you're shifting or were you going over a bump when that sound occurred? If its happening when you're shifting, chances are you need to replace your snub mount. If its "really" coming from the back, I have no idea.

[maccalo]

It occurs only when driving over bumps. It is certainly coming from behind.

[BARRY]

have you peeled back your rear wheel well splash guards and inspected? for the 1.8t b6 a4 in America there is a gas tank evap unit under the rear splash guard.

[diuvic]

have you peeled back your rear wheel well splash guards and inspected? for the 1.8t b6 a4 in America there is a gas tank evap unit under the rear splash guard.

Rear driver side.

[maccalo]

Ok so evap unit is ruled out then? I am 99% sure it's originating from the passenger side.

EDIT: I am unable to replicate the sound when jumping up and down on the tow bar

[BARRY]

on the USDM B6, the passenger side contains nothing under the splash guard. i'd remove it to confirm as you're in a different country. beyond that if you get your car up on a lift and load the wheel any force you apply to that side would probably allow you to reproduce the knock wheel bearing included.

[maccalo]

I'll need to do a closer inspection with the car on a lift.

But can a worn wheel bearing make such sound/knock/clunk, and only when there's a sudden change in load on the suspension?

The best way to describe it is as a baseball "jumping around" in the fuel tank x1.

[BARRY]

a bearing should make a different tone. it honestly sounds like your splash guard is lifting off then hitting your body as it is a hollow sound.

either that or your rear cross member bolts are loose.

[john_gonzo]

Exhaust bumping body or suspension? Loose lug bolts on that wheel?

[maccalo]

Lug bolts are tight, mud flap and splash guard are all secured. I tried to give the exhaust a few taps with a rubber mallet and it seemed to stay in place. Upper strut mounts OK.

I was thinking crossmember bolts, as that has been a known cause of trouble in other VAG models, but could not find something specifically for the A4 B6 quattro?

[john_gonzo]

The video shows what looks like aftermarket audio equipment. Is that stuff mounted solidly? My other thought was maybe the alarm siren came loose.

[maccalo]

Yeah that amp is mounted solidly, and the sound existed before the audio install :) thanks for input

[BARRY]

if the car is on a lift you can easily see the 4 rear cross member bolts. i'd recommend loosening all of them, then tightening all of them again if you're worried. this may affect wheel alignment though.

[maccalo]

My car needs an alignment anyway, I just want to swap out any parts that are worn first (such as recently replacing shocks).

Is it possible to remove the RARB and go for a test drive to rule out that as a cause, or would that not be recommended?

[maccalo]

So I removed my RARB and had a little drive around the block. The knock or clunk is still there .

EDIT: Retorqued subframe bolts (4x 18 mm) - no difference

[BARRY]

does your rear spring contain rubber isolators? i just realized that spring coils when they touch "can" make a knocking noise. the rear spring mounts at the lower arm should contain a rubber spring locator/isolator if i recall correctly.

[maccalo]

UPDATE: Problem solved





The solution was to change the rear strut mounts, bump stops and dust covers. Although my strut mounts looked seriously ill, I think the biggest problem was that the bump stop was moving freely up and down as shown in the video:

[diuvic]

Nice man! How much was it all together to fix? Also, did you make sure you didn't also need new shocks?


Sent from my iPhone using Tapatalk

[old guy]

Glad to hear that you found the problem. However it appears that you replaced a sport bumpstop with a standard one. The sport bumpstop is about 3/4" shorter than the standard stop. It will work OK but it may make the rear a bit stiffer over any bumps since it will bottom out with less travel on the shock.

[maccalo]

Replaced the shocks a few weeks ago, but I guess I didn't realize in how bad condition the other parts were.

Strut mounts $30 each, and the bumpstop / dust cap kit was $40 for both L+R.

Glad to hear that you found the problem. However it appears that you replaced a sport bumpstop with a standard one. The sport bumpstop is about 3/4" shorter than the standard stop. It will work OK but it may make the rear a bit stiffer over any bumps since it will bottom out with less travel on the shock.

The OEM bumpstop was just very compressed after all these years, I checked the part#, and they're supposed to be 135 mm new (which the new ones are). I have non-sport suspension.

Sport suspension kit


Non-sport suspension kit


Notice 2 vs. 3 narrowings

[john_gonzo]

Congrats! Nice work in tracking this down. And thanks for posting the comparison pics.

[BARRY]

that was actually my first guess but as you've mentioned the shocks are new these items should have been inspected and replaced as they do look beat to death.

[maccalo]

that was actually my first guess but as you've mentioned the shocks are new these items should have been inspected and replaced as they do look beat to death.

Thanks for your help anyway Barry. I should have mentioned that I did not change those parts at first, but lesson learnt!!