I'm going out on a limb since you say the car was hit and repaired on that side, but here goes. I had the very same problem on my ex-535is that drove me crazy which made me replace upper shock mounts, dogbone links, rear subframe bushings, removed complete back seat with still no root to the noise. Ended up being the door latch striker, take black electrical tape and wrap a few times the striker on the car where the latch claps to when the door is closed. If this works than you need to get your striker/ latch aligned.