I had a hollow thumping sound from the rear of my camry, and I did two things, so I can't honestly say which one fixed the problem. But here's what I did:
1) Replaced rear end links (found a set on ebay for $30 shipped, 1 year warranty, took 10 minutes to replace).
2) Removed sway bar bushings, wrapped sway bar where bushings sit with a lot of teflon tape, then sprayed the inside of the bushing with lithium grease, then reinstalled. The teflon tape made the bushing fit tighter around the sway bar.
My old end links did not look bad, nor were the joints loose, so I think that my biggest fix for the problem was the sway bar bushing tape/grease. I did all this after I took it to a mechanic who said that nothing was wrong with the rear of my car and said that it's 15 years old, it'll make noise... Well, after doing the two things above, it made the noise go away.