weird clunk sound when breaking

its a 98 explorer , breaks are all new . doesnt feel like its in the breaks at all tho , breaks are perfect . but when im slowing down and its probably 4 outta 10 times but i hear a clunk from the back sounds like from the rear or driveshaft ( driveshaft is tight with no play at all ) but it kinda feels like its down shifting and catching slack from somewhere .. sometimes i notice like 2 clunks , it'll hit then a sec or 2 later it'll hit again .. any ideas? anyone have this problem... tommorow im gonna try coming to stops with it in neutral ... until then, thanks