Check the exhaust bracket underneath the car by where your armrest would be about. Mine broke and the exhaust sat on a brace which made a knocking noise every now and then. I just had the muffler shop use a pry bar to push the exhaust up, then weld the bracket back while on the car, and the noise went away.

 

I put her up on ramps and removed the plastic transmission covering so I could get a good look. All seemed fine. I banged on the exhaust, there was no rattle nor was it coming into contact with anything. I tried to shake the transmission and it was tight. I then banged on the driveshaft with my fist and heard a what I can only describe as a "clink" (not quite a "clunk"). I'm not sure if this is the noise I'm hearing in the cabin. I tried to see if it was the center bearing, but the bearing is hidden under the cats and heat shields. I'll have to investigate further at my clubs next DIY day when I can get it up on a lift.

 

Did you look and see the exhaust brackets? Mine did not make any noise when I shook or banged on it. The exhaust didn't move much at all when I tried. I got lucky and found the broken bracket when I look at each bracket from the mufflers forward. I did not remove any under covers. I was about to replace the guibo which I can now hold off since mine was found to be good.

 

check your sway bar end links, both front and rear.

does the M5 have a guibo? if so, check it.

also check your driveshaft center support.

 

I had what sound to be exactly the same symptoms. The clunking can be quite violent sounding. Turned out my rear balljoints were shot, new rear wishbones going in next week which will sort the problem.

 

it might be number 7

 

Check the colour of your centre exhaust mount rubbers, if they are red, bin them and get latest black items from BMW - about $15 / £10 each - can be changed - just - without pulling the exhaust system. Can cause many a strange noise / vibration through car when worn. The redesigned items have large buffers fitted to stop exhaust collapsing onto floor brace.


Phil

 

Check the colour of your centre exhaust mount rubbers, if they are red, bin them and get latest black items from BMW - about $15 / £10 each - can be changed - just - without pulling the exhaust system. Can cause many a strange noise / vibration through car when worn. The redesigned items have large buffers fitted to stop exhaust collapsing onto floor brace.


Phil

Phil,

Is there any chance that you have a part no handy for these black rubbers? Thanks in advance.

Tim

 

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Was this one ever resolved? I have a very similar 'thunk' LOL...

 

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Was this one ever resolved? I have a very similar 'thunk' LOL...

Me too - and I think it is the exhaust, as the "thunk" is much less once the exhaust has gotten up to temperature (expanded) but still need to have it checked (Frits, here I come... )

 

I had an e39 M5 and had a clunking sound that sounded very similar to what is described in this thread. The dealership told me that there is not a lot of clearance at certain points along the exhaust and as the bushings and other parts get older the exhaust can hit at these points. I don't recall is they needed to replace bushings, and I think I remember them sayings something about shims, but it was not an expensive repair.

 

Sorry for the delayed response, but I've been pretty busy. As of today I have fixed this, and although it was hard to figure out, it was easy and cheap to fix. Most of you should not have this problem, as this was caused by a crappy body shop repair. Back in January I was rear-ended by a 22 year old who thought he could drive while texting. :grrrr: Part of the damage to my car included the mufflers. The shop replaced every single part in diagram A.

While changing out those parts, they removed and re-installed the two long suspension rods (#18 in diagram B) that connect on one end to the rear axle carrier, and the other end to the exhaust mount (#5 in diagram A). Upon reassembly, they failed to install the screws (#5 in diagram B). When I would go over bumps and these long suspension would spring up and down, and as they did they would cause the exhaust support to hit the exhaust pipes, which are just about under the center arm rest.

Two new screws installed and no more thunking.

Diagram A: RealOEM.com BMW E39 M5 Exhaust system, rear

Diagram B: RealOEM.com BMW E39 M5 REAR AXLE CARRIER

 

Glad you got it worked out. Did you mention to the shop that did the work that they left out the bolts?

I too had the clunking noise last year and found that the center exaust support bushings were shot, so I changed them. But I also noticed that the support straps for the gas tank on each side looked like they could come into contact with the "suspension rods" where they met. So I cut a piece of 1/8" thick rubber about 1 1/2" wide and 10" or so long and fit it between the rod and tank strap using wire ties to secure the rubber the rods at each end. Considering the amount of effort to get that 1/8" rubber in between the two, I am confident that some of my noise was coming from this area as well. Attached is a before shot of the area in question, I'll see if I can find an after pic on the other computer. Yes, it is rusty down there....

 

Did you mention to the shop that did the work that they left out the bolts?

I've already had words with these folks, so I felt if I took it back to them they would just grab some bolts out of their coffee can and do more damage. The bolts are only a few dollars and installation took 5 minutes on a set of ramps. I also have the peace of mind knowing it was done right.

 

The clunk is the center exhaust bushings - it might feel tight when you jack up the car and check, but this is the problem.

Replace the bushings with the new black bmw bushings.

Cheers,
Andrew

 

My exhaust bushings are both new.

 

I found this thread usefull as I had a lot of cabin noise. Getting under the car to inspect the rubber exhaust mountings in the centre I could see they had compressed ( old red Type ) and the exhaust was contacting the cross member/ brace under the exhaust. I purchased the upgraded black rubber mountings and put everything back together. My 1st observation is that its so much quieter now almost like new compared to how it was before.

My problem though is that I still do get a slight contact though when cold and can feel the vibration through the arm rest, I took another look underneath and both rubber mounts are compressed very heavily with both squashed against the bump stops.

I am concerned it will just degrade over time and I will be back to square one.

Is there any way I can get some more height on the exhaust I still need about another 1/4 - 1/2 an inch increase in height on the centre. Right now I can just pass a bit of thin card through between the exhaust and the cross member / brace.

Thanks in advance.

Regards
Chad

 

Is there any way I can get some more height on the exhaust I still need about another 1/4 - 1/2 an inch increase in height on the centre. Right now I can just pass a bit of thin card through between the exhaust and the cross member / brace.

Chad,

Even after my repair, and with new mounts, I to still get the occasional contact. My plan is to one day buy some steel washers (spacers) and place them between the body and the mount, effectively increasing the space between the mount and the exhaust pipes. I think all that may be needed is about a quarter inch more distance to permanently solve this issue. If you try this, please post picks.

Regards,
Tim

 

Tim,
in the end I went to my local B&Q hardware store and bought some washers and new longer bolts and it has done the trick nicely. I used some decorators masking tape to hold the washers together so they did not fall all over the place while trying to slip them between the exhaust cross member and the body.

Pics as requested.

Regards John C AKA Chad

 

BRAVO! This is exactly what I plan to do. Thanks again for the pictures.