WD-12NBW - LG Washing Machine Service Manual (repair manual). Page 22

Have all the transit bolts and base packing
been removed?

Remove the transit bolts
and Base packing.

Move the washer or
reinforce the floor.

Is the washer installed on a solidly constructed
floor?

Check if the washer is perfectly level as follows:

Check the leveling of the washer with a Level
and check that the washer is stable.

Put an unbalance part (rubber) inside of drum
and start QC test mode and run in high spin
(Refer to section 7-2). 
When the machine is spinning in high speed,
verify that it is stable.

If you do not have the unbalance part, put 4.5 to
6.5 lbs (2 to 3 kg) of clothing. Once loaded,
press power, Rinse+Spin and the start/pause
button in sequence.
When the machine is spinning in high speed,
verify that it is stable. 

If it is not stable, adjust feet accordingly. After
the washer is level, tighten the lock nuts up
against of the base of the washer. All lock nuts
must be tightened.