A "clonk" is most likely to be the wishbone arm bushes. With the car on stands, you may be able to get under the wheel arch and visually inspect the bushes, particularly the rear one.
If it looks visibly old, crusty, damaged or tired, it could be knacked. A garage will get a pry bar (a 2ft long screwdriver, more or less) and attempt to lever the arm away from the subframe, by putting leverage on the bush.
If there is a lot of movement, then "on the road" the pin inside the bush will bump against the inside of the arm (the rubber won't be cushioning it very well, any more) so you hear the "clonk".
If the bush has been dying for a while, you may see inner shoulder wear on your tyres, since a saggy bush will increase the wheel camber, so the wheel tilts inwards more than it should, and the inner shoulder suffers. If you can get a sometimes "free" camber/wheel alignment check at the local tyre place, that will confirm the camber angle... though if you replace the wishbone arms, you would need to get the wheel alignment checked again as good practice.
Have a look at the drop links while you're there (as above, they're supposed to have no movement) but these are pressed into a nylon bush so last a lot longer.
Springs (when broken) can make a clunk, so have a look at both sides and see whether they look the same - the broken piece usually falls out and that side becomes a little soggier).
Otherwise it could be the suspension top mounts.. but (apart from 500 may be more weedy) I've not had too many dramas over the years, from similar setups. If you unbolt the damper from the hub you may be able to wrestle it backwards and forwards a bit, listening for any noise.
Ralf S.
