raise your car up on jacks, try to wiggle the whole wheel, if it wiggles at all its a wheel bearing, next get up under and try to move your axels, if they move , possibly could be stripped splines, impropper adjustment of axel length, worn cv joints, just a few things to check, most prob either wheel bearings or cv joints...

oh check your driveaxel nut also....about all i can think of right now.

*edit* if your brake disks are warped it will do it also, but you would feel that when you apply your brakes