If you had it rebuilt twice and the noise hasn't changed, it's time to look elsewhere......
I would take it to another shop next, what ratio is it? Why does it have an earlier pre1965 rear end in it? 1964 was the last year Mopar used tapered axles in the 8 3/4 rear ends, 1965 and later should have the later style flat flanged axles in it without the tapered axles
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
