Chevrolet Camaro 1967-2002 - noisey rearend

my rear end only make the noise when im on a curve or coasting without pushing on the gas....when ever i push the gas pedal it goes away...seems like when i hit gas its tight and when not on gas its loose...what could it be? ive herd maby wheel bearings and maby rearend needs shimmed...so not sure...also any time i wanna shift fast 3rd gear wants too grind when going into it...if i shift slow its fine..i was told the skip shift was deleted but the light comes on so i think its still hooked up..is the skip shift causing the 3rd gear sound..if i skip 2nd gear and go too 3rd it sounds fine...its a 98 ws6 that sits alot with low miles... just relized i posted in the camaro forum...my bad not sure how that happened

sounds to me like your 2-3 syncro may be on its way out on the tranny, and your rearend is wore a little, you could probably fix by shimming it up.