When you push the start button, the dishwasher lights go on. The dishwasher sounds like it's starting but after about 20 seconds the clean light comes on. I have found that if I wait maybe 15 seconds after pushing the start button and then open and close the door, the dishwasher cycles normally. Usually when I open the door I hear a hissing sound like a dry pump is running. And the other thing that is strange...once in a while it runs normal without my having to open the door. What's going on here?