Have you checked if there is any oil in the diff? It should be just up to the bottom of the filler hole. Undo the filler when cold and stick your finger in. You should be able to feel or see when you take your finger out again if theres oil in there. I know my LSD is making noises and the oil is low on it. It's got a leak from the front seal. That's one quick easy inexpensive check to be done first. Hope that helps...
EA Fairmont Ghia : 3.9L MPFI, 2.5" cat back sports exhaust, K&N panel filter. Pioneer head unit, pioneer 4" three way fronts, Pioneer 6" 3 way rears, 2x 12" subs, blue interior light.
My main pride and joy : '76 XB Fairmont GS, 250CI, 140,000 Km and all stock.... for now! (Factory air-con on the way)