Clunking / Thumping Noise From Rear End

[PARZ M3]

Alright so the other day I notice a thump, thump, thump noise when I pull onto the Highway and I'm not on the gas (not under load) - coming from the drivers side rear. As soon as I touch the gas peddle the noise goes away. So I get home and check the following things.

Jack the car up and see if the wheel is loose or has any movement to it when pushing on the top or bottom. - No Movement

Check the shock tower mounts even though they have already been replaced. Those are good.

Remove the wheel and start looking around for anything out of the ordinary. Can't find anything that is missing, loose or cracked.

Check the the drive shaft and it looks to be centered and firmly in place.

Not sure what to do next, except to start taking things apart - which I don't want to do. It's definitely motion related as the noise will increase and decrease in speed as the car is moving.

So I turn to the internet in hopes of finding my answer - nothing yet.

Thoughts?

[Inicent Child]

Try using a pry bar between your diff and your diff casing. If it is not solid and moves a bit then most likely your front diff bolt is bent and may soon snap.

[AlaskaBimmer]

Mine clunked on acceleration and then went away, and then a while later it cluncked all the time, which was right after the diff bolt snapped off....

Then it I had to pull the diff out to extract the broken bolt since there isn't engh room to do it in the car... I also went ahead and changed all the diff bushings since it was out, I have a friend with the right tools to press in and out the bushing under the car.

So hopefully you fix it before it breaks, it becomes a much larger problem if you don't fix it right away.

[PARZ M3]

I'm going back under the car today and let you know what I find... I just want to figure it out already, it's annoying not knowing.

[ChuckDizzle]

+1 for a diff bolt (bent/loose/already broken)

[Relax]

Check your e-brake. Mine was clunking pretty bad and or was due to a loose e-brake.

[M3amazesme]

It's probably not this but I chased down a 1 year rattle/clunk finally after a year and I had to rebuild my rear calipers.

[clytle]

+1 on diff bolt. I'm on my third. modified a grade 8 construction bolt and washer to fit. works like a charm

[NakedBeast]

Rear shock mount.

[arthothezilvian]

Might be your Rear Shock Mounts. Mine clunk so much. I have to replace them, but I'm waiting to get coilovers and just do it all at the same time.

[PARZ M3]

Negative on the Shock Mounts - E46's with Z3 reinforcement plates / maybe blown struts? But it's rotation related and only makes the noise when coasting, clutch depressed etc so I don't think it's that though they need to be replaced.

Front Diff Bolt is on Tight with no apparent damage. I cannot get the rear end to budge with a pry-bar. All of the bushing look to be in good shape also.

[Relax]

Negative on the Shock Mounts - E46's with Z3 reinforcement plates / maybe blown struts? But it's rotation related and only makes the noise when coasting, clutch depressed etc so I don't think it's that though they need to be replaced.

Front Diff Bolt is on Tight with no apparent damage. I cannot get the rear end to budge with a pry-bar. All of the bushing look to be in good shape also.

Try checking your e-brake like I said. I had the same issue, everything else was fine. Found out that the E-brake needed a little adjusting and bam, the clunking sound was gone.

[joshduck]

Did you discover the cause of the problem? My '01 Z3 seems to have the same problem. It seems to be worse when I ease off the gas, like you described in your original post. Thanks.