This kind of clunk could be caused by a lot of things, as mentioned above. Hopefully it will prove to be something simple to fix for the caller. But if not, here's my 2 cents for what's it's worth:
I have a 1970's Ford 4wd truck w/a similar clunk. I'm told it is a normal sound. It's caused by the way the truck is designed, specifically by the limited slip rear differential slipping normally. Sometimes it doesn't slip until a few seconds after the stop, when I notice a clunk and the car seems to move a bit. I sometimes notice a similar clunk on start up. And I notice an even more noticeable clunk when I put the truck in reverse. All this clunking is worse with an automatic transmission, and worse with higher idle speeds. If you notice this kind clunk and your vehicle has a limited slip differential, one thing you can do is make sure the idle speed(s) are set correctly.
If the clunking gets worse, that's a sign -- at least for my truck -- that the one of the drive shaft u-joints may be failing (between the transfer case and the rear differential, usually it is one near the differential) . A mechanic can easily diagnose a failed u-joint, and they are fairly inexpensive to replace. Or it might be simply that the u-joint or the splined joint in the drive shaft needs a shot of grease. Oh, one more thing. If there's been any work done one the differential, one other possibility is that the mechanic didn't put in the req'd amount of friction modifier additive when they replaced the differential gear fluid.