When my rear end started to make that noise it was the rear-track arm control arms. There is really no way of checking them cause the play that the bearing cartridge develops is as thin as a hair but can cause ALOT of clunking and chattering from the rear end when going over bumps.
http://986forum.com/forums/showthread.php?t=9581
http://986forum.com/forums/showthread.php?t=11446