...perhaps you may try relieving the trunk of spare tire, tools, etc. and test again as one of these items may be the source

>if you have a CD player mounted in the trunk, you may wish to check if the mounting are tightened properly

>also, if your spare is not tightend down, this may be cause of the clunking as you go over bumps

>on a more technical note: you may also wish to inspect: rear subframe bushings, rear chassis mounts/ supports, exhaust system hangers (rubber donuts/ metal ears)

hope this helps, and let us know what turns out

-fad