I have been having the same issue. An occasional clanking in the right rear, usually at low speed. I too have checked under the car for anything loose or rubbing and have come up with nothing.
I am planning to replace the original shock mounts with the new upgraded Performance Unlimited mounts. I was thinking that might be part of the problem...even if it's not it looks like a good upgrade.
Thanks for the tip about the trunk support Blas. Although it doesn't sound like it is something that lightweight. I will check that tonight.
Bob