Sounds like something is off balance

Years ago had similar issue with 7 1/4" rear. Sounded like right rear.
I balanced drive shaft, not it. re balanced all wheels, not it. Replaced rear wheel bearings, not it.
Switched axles one side to other. Sound moved to drivers side.
Went to junkyard picked up another axle......Noise gone.
Ever so slight bend in axle. I couldn't see it.

People give those rearends away nowadays. Id swap it out with another.
Cheapest thing to do instead of replacing bearings in carrier etc.