Park the car on a flat surface. Then with the shifter in gear or Park, rock the car forward and aft and look for play in the driveline. If you don't find much play, raise the rear wheels and try to rotate one wheel while resisting the opposing rotation on the other wheel. By doing this you might observe some play in the cv joints or in the differential case.
I located a clunk in my '79 this way...a worn spider gear shaft. The PO must have gotten it stuck and never bothered to read the owners manual. Anyway, a switch to 90W140 gear oil quietened the clunk quite a bit.