Typically, when the car is moving forward, any play in the suspension bushes is taken up, and all is reasonably quiet. However, when the car is stopped and then reversed, the play (or slackness, if you like) shows itself in the form of a clunk.
Now, there are many suspension joints that can clunk, but I'd play particular attention to the bottom swivel joint (wishbone to hub, at the very bottom) and then the inner wishbone bushes themselves, especially the rear one. When you are in that area, do check the springs for broken coils! Very common, that one.
Another suspect is the drop link or stabiliser that connects the front strut to the anti roll bar.
A popular method of testing bushes is to get a lever close to the rubber bush, and testing for any movement by moving the suspension component up and down.
Other things could make a noise too though....front brake pads can move about a little, and rear brake shoes can come off the drum with a clang. I do suspect suspension issues with your car though.
John
