Whining Noise When Letting Off The Gas

I need some help with this one. When I let off the gas I get a whining noise that sounds like its coming fom the rear end. The sound is not there when i am on the gas. My old rear end was a 7 1/4.This is the changes to the rear. i will list everthing to help with the troubleshooting.

- rebuildt 8 1/4 321 with suregrip new seals and bearings
- 11 x 2 inch drum brakes
- shortened drive shaft 1.6 inches
- 17 inch wheels
- 5 pack hd leaf springs
- Firm feel sway bar
- firm feel front hanger using top position to lower car 1.5 inches

Thanks for the help