Originally Posted by Sluggo
but one that was not mentioned is the possibility of failing BB bearings
I once took apart a bottom bracket that had an occasional clunk, and found one ball bearing that was sheared in half. It would turn smoothly as long as the two half bearings stayed out of each other's way, but when they got together wrong it went clunk.
Not that that's what's wrong with yours, 'cause I've only ever seen that once...just sayin'