Clunk from rear end.... Anyone else have this?

When I reverse the XJ and put it in drive too fast, I get a clunk from what sounds like the differential. If I put it neutral for just a second, then drive, the clunk is non-existant. I haven't really inspected my driveshaft, but I suspect it's a U joint. I was wondering though if this is possibly a damaged differential? People have told me it's normal play in the driveline, but this seems to be a little far fetched. It doesn't really ever cause problems once moving forward though. Any thoughts?

How long have you had the Jeep? An automatic locker would sound like that but you'd probably know if you had one. Other than that, check the u-joints on the driveshaft.

It may be U-joints, carrier bearings or just a combination of worn parts. If the U-joints are OK, the carrier bearings OK and the spider gears (and thrust washer) OK, I ignore it. My 88 Chev, did that from day one and for the next 200,000 miles, never seemed to hurt anything.