Please help ASAP

I've been on many forums with this question with many different answers but none seem to fit as a solution to my problem. I have a '04 mustang gt auto; at high rpms on or off the gas when it shifts i hear a squeal in the rear end. I know its not the tires breaking free, so i am leaning towards the gears. What maybe the problem?

Aswell when just crusing at any speed and you give it a shot of gas i hear a big clunk in the rear, which makes me lean towards a bad u-joint, Which i am 90% sure it not a major problem.

So if anyone has an idea what could cause this squeal, info whould be greatly appricated. Thanks.

Are you sure it is the rear end? It could be your trans as well. Mine is doing the same thing (87 Mustang) and my overdrive is acting up. Just a thought.

Check the u-joint. The needle bearings could be bad.