First make sure the unit is leveled properly and the drum is centered. If the UE error is not due to a leveling or laundry balance issue, then run test mode and check for out of balance in high spin test.  If unit is still is out of balance while empty, then check for foreign objects under the pulsator or between the tubs & make sure unit is installed on hard level floor & inner basket is not warped. Check for cracked magnets on rotor as well as tub & rotor & pulsator nut for tightness & check for when a load of 6~8 bath towels is placed in the unit & filled with water if tub leans to one side, may need to replace the suspension rods & inspect balance ring for loss of fluid.  Check Pulsator & Clutch & Tub splines for worn.  If clutch assembly is worn or making grinding noises, then unit will need a new clutch assy.  If still has constant UE errors and none of the above apply, then replace the rotor.