From 62-70 mph the rear end of the car gets so loud you can't talk over it. no "clunks or thunks" just gets loud - sorta like a kitchen mixer turned to high speed, only much louder. Don't know the car history, but it has 97k on it and a "towing package" with tow bar and "adjustable air suspension" (flip a switch) No noise at lower speeds, and no vibration.

Sounds like you have a bad bearing (axle, pinion or carrier sides) You need to do some further checking to determine which. Low differential lube level will also cause a noise but if you've driven it that way for any length of time the bearings are likely ruined and possibly the gears too.
Aside from axle bearing work, anything inside the diff will be very expensive and generally your best option would be a used one from a scrapyard. Sounds like you have a bad bearing (axle, pinion or carrier sides) You need to do some further checking to determine which. Low differential lube level will also cause a noise but if you've driven it that way for any length of time the bearings are likely ruined and possibly the gears too. Aside from axle bearing work, anything inside the diff will be very expensive and generally your best option would be a used one from a scrapyard.

Thanks. We'll look into the bearing asap. Your input was really appreciated!! Thanks. We'll look into the bearing asap. Your input was really appreciated!!