DIAGNOSIS Persistent musty odor is caused by biofilm and mildew growth inside the machine, typically in three areas: the rubber door boot gasket (not applicable to this top load), the detergent dispenser, and the hidden sump area beneath the wash plate.
FIX Execute a full cleaning regimen. 1) Remove the wash plate by turning it counterclockwise. Soak it in vinegar. 2) Wipe the exposed stainless steel basket and the area under the plate with a 10% bleach solution. 3) Run a cleaning cycle. Select 'Clean Washer' mode. Use a washing machine cleaner tablet (like Affresh) or two cups of liquid bleach. Run with hot water.
IF THAT DIDN'T WORK If odor returns quickly, the drain pump filter is likely harboring debris. Clean it as outlined in the leak procedure. Also, leave the lid open between washes to allow the tub to dry completely. Never close it on a damp tub.
HEADS UP Using fabric softener liquid or sheets significantly accelerates mildew growth. They leave a residue that coats the machine and fabrics. Discontinue use if you have recurring odor issues.