Sound effects would be nice on here.
On my Cutlass I had kind of the same scenario. If you backed up and stepped on the brakes you would here a "clunk" when you went ahead and stepped on the brakes, it would clunk again.
I had checked everything and not a thing looked wrong. Until I decided to upgrade the suspension bushings. One of the lower control arm bushings seized in the rubber causing the metal shell to rotate on the bolt going through there. Must've been like that for a LONG time because the bolt was worn half way through! Thank goodness I decided to upgrade the suspension!