clunking when you get off/on the gas, like the classic rear diff clunk, right?
the next suspect is the subframe itself-- check that it's properly and tightly attached to the underside of the car. go through each of the bolts and check the torque. If okay, then check the subrame bushings-- when were they replaced, if at all?? there's definitely subframe movement causing the clunking, then you have to check all the possible places where movement can occur...
any way you can attach a video cam down there and drive to see where and how much movement you are seeing?