C4 auto shifting noise

[dave]

This is a 90 corvette auto trans. with 46K. This car drives strong and smooth with no vibration at any speed. The problem is there is a clunk from the rear end when shifting from 2d to 3d and again when downshifting from 2d to 1st. When excelerating hard there is no sound heard. Does the same thing when manually shifting 2d to 3d. All u-joints check good,all rear susp. bushing have been replaced,C-beam is tight,hub nuts retorqued,fluid in trans and rear end have been changed(with additive),diff. gear back lash checked. Several Mach.(independent and GM corvette Mach.) have inspected and can't identify the source of the problem. It also has a louder pop or clunk when shifting out of reverse but only when cold. Seems to go away after warming up. Can't really decide if the problem is in the trans. or the rear end. Any help or ideas.would be much appreciated.

[Mark Dalton]

This sounds dumb and I can't see how it would tie in but, are all the exhaust components tight? Clamps, pipes, etc. Not sure why it'd do it only when shifting but....

[fletcher4u]

check the splines on the slip yok and output shaft for lube and ware maybe binding.