ok, if the wheel moves in and out, you have a huge problem, the wheel it self could fall off. most of the time a wheel bearing is not that bad.the easiest way to find which bearing it is, is to "load" each bearing. what i mean by this is turn your car to the right, to get a majority of the weight to the left side of the car. If the noise gets louder when you load the left side(turn to the right) than the left rear wheel bearing is bad, if the noise gets quieter, than it is the left. do the same thing turning left(loading the right side) if the noise get louder it would be the right rear, and if it gets quieter, it is not the problem.
it is posible to have both wheel bearings go bad, so if it gets louder while loading either side, then it would be both.
hope this helps, good luck,
Schubs