OK...so you're going to think I'm nuts, but here goes.
Going over bumps led to a distinctive clunk coming from the left rear.
After some investigation, and by this I mean I removed the interior panel on the left rear and found a couple small holes through to the space occupied by the top of the strut. Bouncing the rear of the car led me to see the top of the strut moving up and down. Thinking this should not be, as I've never seen the top of a strut or shock move up and down, I removed the strut assembly. There is a dust cover on top that was all tore up with holes through it in several places. The top threaded part of the strut was not alligned with the top of the assembly and the top washer looked to be on upside down.
Online, I purchased the two top bushings, spacer, large metal spacer and bounce absorber and took it all to my mechanic. He took the strut apart and replace said parts being sure to install the top washer right side down. I reinstalled the strut and the noises ceased!
The struts were replaced by a dealer at 29,500, and the clunk started shortly after. We are now at 45,000 on our 2007.