Best thing to do is jack up the rear on axle stands and get a pry bar or bfo screwdriver and lever all the bushes about you'l be able to see them moving and find the culprit.
Rose bushes knock a bit and can sometimes creak so give them a good lever about to see any play in them.
Trailing arm bushes are also common and can be felt when cornering as the back end gets twitch and feels like its moving around.
ARB bushes knock and can also creak as well as the drop links.
Hope this helps.