1997 BMW 528 Clunk noise from right rear

Noises problem
1997 BMW 528 Automatic 80,000 miles

When going over slight bumps, especially when turning right there is a quite loud clunk noise from the right rear. It sounds like there's a hard heavy object loose on the trunk floor. I've replaced the wheel bearing (which needed replacing) and the sway bar links because one had some play but the noise did not change. I took everything out of the trunk and checked to make sure the battery was very firmly fastened down. No change. I've yanked on and banged on every suspension part with a rubber mallet and cannot find a worn or loose component or a matching noise. The exhaust system and gas tanks also appear to be very well mounted. I'm baffled. Any suggestions for what to check would be greatly appreciated.