banging over bumps in left rear of 98 C230

[White951]

The car has 110k miles. When the car is driven over a bump there is a bang in the left rear of the car. I sat in the back seat on the left side and it comes from behind me not under my but. I backed it up on ramps and pulled on the exhaust and the suspension and subframe but nothing appeared loose. While it was on the ramps i put a jack under the left side and raised it a bit to see if there was any play in the subframe mounts when I jacked it up but there wasn't any. The rubber on the mounts look intact. Rear shocks are bilsteins with 50K miles on them. The shock mounts in the trunk are tight. Seems more noticeable in the winter than summer. Bounce test on the rear settles down right away. Removed the spare and sound persists. battery is bolted down (right side). The coil spring looks OK also. Anyone run across this before or have any thoughts?

John