Well, it looks like you and dgc333 have discovered the achilles heel of the 833 OD aluminum case tranny. The noise you are hearing is excessive lash in the gears caused by wear in the countershaft bore in the case. The front end of the countershaft rides in a hole bored in the front of the tranny case (no bearing). This is sealed by that little freeze plug looking thing about 2" below the input shaft.