Do you still have the factory axle Dampers on? They are two solid Iron weights at the end of the axle that mount to the lower control arm brackets. I took mine off when I did my suspension, and took the car out today and had the rear end whine for the first time. I will be putting them back on after I coat them in POR15.
Just another thought. They were put there specifically to reduce the whine or 'ringing' of the rear end. If you need some, I guarantee there are guys who are willing to give them away as most tinkerers take them off.
08' HG #1551
My Road Course Toy
BAMA Tune, Pypes OR X-pipe, Stock Mufflers, Tokico D-Specs, Motorsport K-Springs, Eibach Pro Alignment Adjustable Rear Control Arms, J&M Camber Plates, J&M Adjustable Aluminum Panhard Bar, Whiteline LCA Relocation Brackets, Whiteline adjustable front Swaybar, Stillen Adjustable rear Swaybar, Steeda Bumpsteer Kit, 19" Brembo Wheels, EBC Yellows.