Rear end noise ?

Well i just took the Dart out for a road test after installing an 8 3/4 323 sure grip clutch type.It has a noise kind of like a 4 speed wine if you know what i mean,when coasting, but with my foot into it nothing.The axles had new bearing 2000 miles ago,newly installed U joints so one would thing thats not my problim,the last pig had no noise.This pig sat all winter with no gear oil.it has new 75/90 gear oil and ford friction modifier now.Any thoughts did i buy junk. I guess i could turn up the tunes and drown it out lol.