2002 Ford Explorer

Noises problem
2002 Ford Explorer 6 cyl Two Wheel Drive Automatic

My car has 80k miles. I hear a noise from the rear end that changes with the rpms. It sound like, if I were driving nest to a truck with large tires, that trucks tires rolling down the road. The noise does not change when I am turning corners. One shop says "new bearings" for $700. The other shop say "rebuild rear end" for $3,000. Any guidance would be greatly appeciated.