Strange Howl

[exacutionar]

Ive searched threw numerous post and still cant find something that im looking for but Im sorry if this has been answered before. I have built my cougar sv prolly a week ago and since I have had a strange howl comming form the back. I have torn apart my diff 3 times now tryed it right and left positions to see if that was the cause. Loosen and tighten my slipper clutch and still cant find it. Reason im thinking diff is cuse i loose power when it howls.

I did the break in as any ball diff by spining a tire off the ground and back and forth, and built it per simons diff build wich was really helpful. Any help would be greatly appracated thanks again.