Hello BenzWorld, I have been having this issue with my 1990 190e 2.6 that has a 5 speed swap. I swapped the transmission and differential years back and the car drove great. More recently I had pulled the engine and trans and the car sat for about 2 years before I had new seals put into the transmission and the head gasket done to the m103 engine. After taking my time putting this thing back together I now have this random violent clunking that happens very inconsistently. The car made similar noises when my flex disc went out year back but I have new flex discs and new motor mounts in place. After a week of not figuring out the problem, I took it to a shop where they immediately diagnosed bad rear subframe bushings. I had them go ahead and do the job and they installed strongflex polyurethane bushings. After the expensive job ($1500) the car drives better but the loud clunk from the rear end is still there!! I am certain that the noise is coming from the rear end. I am starting to believe that the differential is making these noises. The differential from what I am told is an lsd from a sportline. The differential never made these noises prior to the engine and trans being pulled. The clunks happen sometimes when deaccelerating and also between gear shifts but it is hard to replicate the noise on command. The clunks do not cause any driveability issue but it sounds like bolts smashing into each other in the bac and have no idea what it could be. I have checked the bolts everything seems nice and tight. I am replacing the transmission mount tomorrow to see if that helps. If anyone has any ideas please let me know. I can send pictures or give any details if needed.