I used to get a clunk and a creak going over speed bumps and potholes. turned out to be knackered wishbone droplinks. Replaced with Steve heath rose jointed jobbies, big improvement and worth doing even if that isnt the cause of your clunking.
If the bushes are the oem type and no thrust washers are fitted, the wishbones can move back and forward when the bushes delaminate, which might knock.