Sounds like an axle bearing to me...That would be the first thing I would check....Same as a front bearing..you turn the noise comes in, straighten out and it goes away..
Get the rear tires up in the air enuf to get your hands under it...go side to side and tug up and down...If's theres play..odds are thats your problem....Get new axle seals to as there gonna get wrecked taking em out to get the bearing out......