I've read to lube the bushings?
Mine has done this too, though i live in nowheresville, ga on an unmaintained dirt road. it's a combination mud pit/rally race track depending on rain. I would attribute the clunk to dirt in the bushings. Mine was doing it real bad for a while... i researched it and took the rear end apart 3 or 4 times to find nothing broken, worn, or torn so i just put it all back together and drove it. I ignored it and went through my personally "rally track" a little harder than usual. I figured if i really beat on the suspension, whatever was clunking would break and then it would be easy to find and fix it. wrong! lol. damn car fixed itself. Whatever caused it must have either cleaned itself out going through the big mud holes, or bent, taking up whatever little slack there was that was causing it. Either way it quit and hasn't started doing it again since.
Maybe best bet is to take your car out in the woods or in some rough dirt roads and beat on it, see if you can jump it. worked for me! (piss)