7 1/4 noise

First rear I rebuilt by my self was a SBP 7.25. Anywhere above 40 mph under load it sounded something like a horn blowing.
Carrier bearings, pinion bearings an seal, squash collar, etc... Approx' 150 bucks, oil and all, but that was 35 years ago. Who knows what good quality bearings might cost today. You might buy a entire rear for the same money. That's a gamble too though.
So the first thing to do is have a look at the gears you have. Mine were good ( very little wear ) and it turned out nice and quiet as we drove that car daily for almost 5 years before a LBP 7.25 went under it.