most wheel bearing noises are impossible to recreate on the rack, unless the bearing it really bad. i would be inclined to say the bearing is going bad because when you shift the load, via turning right, the noise goes away. one way to check it while loaded is to drive the car nice and hard, make sure to keep shifting the load, then use an non-contact thermometer to check the temp of each rear hub. if one of the bearings are bad it will read higher.