I would run your machine empty on the hottest and longest setting with maybe 2 cups of vinegar, then run another wash with hot water, and it should be fine. I'd also look at changing the powder, or even changing to liquid as it sounds like its creating a build up in your machine. The vinegar/bicarb trick with each wash should probably fix this as well I'd imagine. Do you use softner? As sometimes this creates soap build up which can cause problems for powder as well.