Having problems with either top or bottom spray arms spinning. It does fill up with water and some water comes from the botton arm but does not have enough pressure to spin. No water ever comes out of the top arm. There is a humming noise that has not been there in the past. I have taking the filter off and inspected the plastic empeller. The empeller appears to be fine but does move back and forth almost 1/2". Is that right? I have also inspected the ball check and it appears to be fine. It does cycle thru the wash but still leaves us with dirty dishes and a clump of soap. The water does drain. What should I do next? I would love any advice. Thanks, Adam