After much input from everyone, I decided to start into the car today and started with the shock. It seemed tight enough, but while I had it up on jack stands, I noticed that this large piece of metal or, for lack of a better word, skidplate that is beside the suspension had come loose. You can see where it has rubbed up against the shock absorber, so I believe this is the source of my strange thumping noise. But thanks again to all who wrote me!! Scott