[jhandy]

for those that may have the same problem;

I have had a thumping in the right rear for about a year now. The problem turned out to be the rear track arm. (199$ from pelican). I noticed about 10K miles ago, a small amount of oil at the rear rubber bearing. When I removed the arm, the rubber bushing was mobile and soft. The new arm had a rubber bushing that I could not move, very stiff.

No more thumping over cobble stone roads. The stearing is more responsive also.
You need an 18mm socket and torque bolts to 118 Flbs.
There is a write up here if you need it,

http://www.6speedonline.com/forums/tech-how/126812-diy-replacing-rear-upper-control-arms-track-arms.html

Total install time was about 1 hour for both sides.