You will most likely be able to hear knocking coming from one side of the car, also if you jack the car up and try to move the wheel and see if there is any excessive play/movement. Is it on the front or the back that you can hear clunking? What car have you got?
Also have a look at your suspension bushes as these can fail on older cars as well and cause these symptoms. Depending on your car put one of your hands on the car's axle and then try to move the axle, if you can move the axle slightly or feel any excessive movement then the bushes are knackered. also look at the shock absorbers & whishbones etc.
Liam