It's something in the back wheels making the noise. Not to many parts to make that when rolling. So check the wheel bearing it's super easy. Jack the car rear tires up to clear the ground doing that. Now shake the tire back and forth to feel any movement. If it moves any little it's most likely a bad wheel bearing. Remove Nd replace. If it's rubbing then remove the tire and look for scratches on the caliper rubbing the wheel inside. Or shocks. If you don't know what your doing goto a shop and let them inspect it for you. Also if you have a tire that is wearing tread off the sides that will be a clue which side it is.

Check rear brakes and that also means the emergency brake shoes that are located under the rear brake disk . and also check the rear shocks