clunk from back end

[niceold600]

when making a turn (from a dead stop) i occasionally get a dull clunk from somewhere in the back end. i am 95% sure that it's not caused by anything in the trunk and the shocks/coil springs seem to be solid. any ideas ?

note that this is a DULL clunk, not like an exhaust rattle at all.

(1986 dodge 600).