Thump Sound What Could it Be?
 

I keep hearing a thumping sound when I go over bumps (small or large) on the right rear side. What could it be? The right wheel seems solid when I raise the rear and attempt to move the wheels with my hands; nothing looks worn or loose underneath

I had similar issue and it was the lower control arm aka track arm aka trailing arm. Best way to test is with it out of the car. Many threads covering this issue. Like most suspension components, replace both sides as they go out one after the other.

+1 on trailing arm...it would be my first guess

I have same issue. Best brand of track arm to buy?

TRW....decent pricing on Amazing when I bought mine a couple years ago...

I agree with the aforementioned comments. Do the rear track arms. I did mine and it worked.

Summit has a good price on the 987 arms (which work with the 986)
https://www.summitracing.com/parts/trw-jtc1316

I am using Cayman rear trailing arms on my 2004 Boxster S.