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Discussion Starter #1 (Edited)
Hey there! Been owning an E46 330xi for 3 years now. I'm one of the many with this problem, from what I've read on all of the forums, but I haven't found a solution yet. The car is 5 speed manual. Whenever I release the clutch or release the throttle pedal and then hit on it harder, there's a fat clunk/thump, heard from the back of the car. For the past 3 years I've tried a few things: swapped all of the bushings, changed the transfer case, changed both front axles. The thump persists, even though it's better now due to play in all of the changed above. I can't find any unusual play now. Today I went with my mechanic to try and see what's happening. I noticed that there's a weird clunk, seems to come from the inside of my rear differential. I recorded a video of that:

https://youtu.be/yV-YPNQvXMU

Does anybody know what's happening and what should I look at to fix that thump? If you're below the car it sounds like a clunk, however, from the inside you hear it as a fat thump. I'm less annoyed by it since I've been driving like that for 3 years now, and I've got the hang of it (how to drive the car with less thumping), but that isn't any fun at all! Is it even a problem from the differential, or is there something else?

Your help and experience will be very appreciated!
 

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You might check your rear coil springs and shocks 1st. The car has way too much play in the rear suspension. The coil springs typically break off at the bottoms of the coil, which are tough to spot unless the wheel is off and your really in there with a light. If you've done the transfer case mount, I'd replace the engine mounts. They should be both done at the same time, or close to it.
regards
 

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Discussion Starter #3
Thanks! I've actually done the springs and shocks as well, 2 years ago, it's the fact that I'm actually on the brake and vigorously releasing the clutch at the same time. I haven't replaced any mounts, I just replaced the transfer case. There wasn't any play in the transfer case mount. I'll be sure to double check the engine mount, but I haven't seen any play there as well.
I found the culprit of the sound, but that's surely not going to fix the thump, since I didn't have that problem before, but still had the thump. The clingy sound is coming from worn out drive shaft. I'll be replacing that in the upcoming week.
Still haven't found a solution about the thump. I've got a transfer case that doesn't transfer to the front wheels at all, basically makes the car RWD, which I'll be putting on when replacing the drive shaft to isolate whether the thump comes from the front or the back.
I'll keep updating this post with everything that I try and find out, because as I know there are many people facing this problem out there.
Looking forward for more help and tips!
 

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Since you know the transfer case is toast, you might address that 1st. When releasing the clutch, can you tell if it's coming from the bell housing below? With AWD cars, one key, is to keep the drive line mounts in good shape. They tend to beat them up. One of the 1st things I did when we got our 330xi, was to replace a load of mounts:
1) motor mounts
2) transfer case mount
3) all exhaust mounts and hangers
It gets rid of loads of noises and vibrations. It also allows you to easily diagnose the more esoteric problems that crop up.
 

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Discussion Starter #5
For the third time, the transfer case is brand new :) I can't tell where it's coming from when releasing the cluth. I don't see any problems at all with the mounts.
 

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Discussion Starter #7
it's just the way they are.....
There must be a reason behind this! I really can't sleep with "it's just the way they are", there should be a scientific explanation on what's actually happening. I doubt that ALL AWD e46s do that!
 

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2005 e46 330xi 6spd
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FWIW, mine does not have a clunk. At all. And I've been listening b/c I'm at the mileage where lots of stuff wears out. Mine's a 6spd too. My motor mounts are two years old, but everything else is original from the factory.

A couple more things I've seen reported as wearing out: center support bearing, flex disks, RTABS, and (possibly) rear subframe bushings.
 

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I have a low grumble under heavy load/acceleration, almost like driving over rumble strips w ear plugs inserted. Put on a lift this weekend and found the csb almost completely torn 360 deg. Parts are ordered. Guibo to be replaced at same time. I suspect both to be original ('05 w 194k miles, 6 spd) based on the condition of the exhaust hardware where the manifold attaches to the midpipe.

I don't experience the clunk you are OP. I have recently replaced both engine mounts as well as the TC mount. The driveline was silk smooth until this issue w the csb arose. Based on the video - does the rear diff bushing have excessive play?

Sent from my SM-G973U using Tapatalk
 

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That's a good point, I'd consider dropping that diff. It's not fun but it's not that bad either. Mostly it's just a heavy PITA.
 

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Discussion Starter #12 (Edited)
A lot of info there, thanks! I'll post an update from today: I went and removed the rear drive shaft and sent it to a shop to repair it. There were a lot of problems with that: the one that I found at the start was a bad u joint at the rear differential. Apparently the bushing in the middle is also torn, and the middle joint has play. Tomorrow I will get my rebuilt drive shaft back and I'll post any updates when I get it back on the car, but I'm feeling confident that this might reduce the thump by a lot. I decided not to put the RWD only transfer case for now in order to test the drive shaft first. I checked the guibo today, it was as good as new. The transfer case bushing is dead by what I saw today, and I will also be replacing that, however this might take a few days, since I can't find any in stock in my country.
 

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That transfer case bushing is my least favorite job on the XI. It's super awkward to remove and install.
 

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Discussion Starter #15
Update: After having the drive shaft repaired and like brand new, I installed it back. I also changed the transfer case bushing. Currently there is no play at all anywhere - not on the diffs, not on the rear and front drive shafts, not on any of the axles. This is driving me mad now. My next theory is that it might be the clutch/flywheel, but that's a big investment to change, considering the clutch has been changed right before I bought the car. I won't do that if I'm not 100% sure it's that. I don't really know how I can diagnose this without putting a new clutch/flywheel in. I surely don't have any clutch slippage or any problems with it, except one thing, but it might be usual for an E46. The clutch is really sensitive compared to other cars that I've driven. You don't need to release it as much as in other cars that I've driven to make contact and start driving, if that makes any sense.
I don't really have any other clues on that case, I've mostly tried everything there is. Might as well put the RWD-only transfer case to be 100% sure it's not from the back, but I currently don't have the free time and can't be left out without a car for a couple of days.
 

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2005 e46 330xi 6spd
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This only occurs to me b/c I had a water bottle rattling around in my trunk this weekend: Is the spare cinched down? Battery loose in the tray and sliding around? Maybe something came loose behind the carpet in the trunk? An exhaust hanger loose and it bangs into things? Exhaust is probably ok though after all the work you just reported. Just spitballing some more!

If its the clutch it should sound like its coming from pretty much directly beneath you in the driver's seat, and I bet you'd feel it through the shifter as well. Can you get someone to drive and you sit in the backseat to listen better?
 

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Discussion Starter #17
It's the same sound if you are sitting on the backseat, you just hear it louder. I will see if I can film a video of the thump while being inside the car tomorrow! I'm pretty sure that's not a rattling from the trunk, since when I bought the car, it didn't have a spare tire or a battery lol, but it still did that thump. I'll make sure to empty the trunk tomorrow and double check that, but it's surely not that.

I forgot to mention that the thump still persists, but it doesn't sound like metal hitting anymore, due to the rear drive shaft being fixed.
 

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Discussion Starter #18
Update: Got my car back after everything done just now. First impression is that the clutch is different now? No idea why is that even a thing, since I didn't even touch the transmission, but it's not as sensitive as before. My bet is the flywheel on the thumping, but I guess I'll just have to wait and see whenever I get to do a clutch work. I'm considering going for a single mass flywheel due to it being cheaper and so that I don't have to do a flywheel ever again on this car.
 
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