Add one more possibility- - - -loose trans to bellhousing bolts- - - - -I've seen it happen pretty often. Bad bearings and/or a worn 2-3 synchronizer is the most common cause.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!