Rear End or Gears?, Maybe Axle spline?

[FormulaLT1]

I have a 96 Formula with Auto Tranny, I bought this car as my second car to make fast and take to the track on weekend's. It has had a New Engine put in(10,000 miles before I got it), New Tranny(right after I bought it) but in stock form except for just external & exhaust mods, and most of the Front suspension replaced. waiting for the weather to warm up here in Jersey before attempting the rear suspension but I do know one of the End links to the rear sway bar has fallen off while I was overhauling the brakes, I have bought the link but as I rarely drive this car I figured I will wait to install it, til I have a warm day. Anyway I was bored with my other car one day last week and decided to go out for a FAST ride and noticed that at low speed's there is a clunking noise coming from the rear and a scrapping sounds around turns, as I am not really a novice at dealing with these kind of problems having owned about 10 or so muscle and sports car's I know its sounds like the Posi Rear but its not giving any of the regular symtoms as the Posi, it can spin both tires equally in rears, Anyway I also noticed that when I stopped the car on flat road and put it in park I could push it about a foot in either direction which kinda makes me believe it's the gear's and its missing a tooth but was just wondering if anyone had another opinion or thought it could be caused by the end link