A few weeks ago I started noticing a clunking sound from the left rear of my C230K. It sounds like metal on metal, and it makes the sound when going over rough, uneven surfaces. Interestingly, it doesn't make the sound going over speed bumps or moderately rough roads. The periodicity sounds like something loose that's hanging down from somewhere - it makes the sound most often when the rear is moving side to side. My thoughts were sway bar links or a broken exhaust hanger.

The rub is - this weekend I took off the left rear wheel and stripped the left trunk liner, and nothing is loose. All the suspension bits seemed firmly attached (both hanging and at ride height) and the exhaust hangers are good. And nothing inside the trunk compartment seems loose.

Any ideas?

Thanks!
Anthony