P.F.
Persistent or returning odor is a sure sign of remaining residue in your washing machine. You need to clean the "splash area" just above the normal waterline. This area invariably has the worst buildup from suds and soiled water splashing up and not getting rinsed out. To clean the odor-causing residue from the splash area simply add a cap of Smelly Washer Cleaner to a full load of laundry. The added bulk of the laundry will raise the water level to include the splash area. To compare washer cleaners watch this news story on youtube.
http://www.youtube.com/watch?v=Ua6OJPn0-fU
Smelly Washer, the original creator of washing machine deodorizer, is the only washer cleaner you're able to use with laundry.