I have a 2005 model Frigidaire dishwasher model FDB1050RES0 It fills OK the goes through its first cycle. When it pumps the water out a loud hum and vibration can be heard coming from the sump pump area. It seems to be dry pumping. If I let it go long enough the pump finally shuts off and goes on to the next cycle. The noise returns the next time water is pumped out again. If you add water to the dishwasher via a pitcher when the hum and vibration starts they will stop but then begin again. Do I need a drain pump? How do I get to the drain pump on this model? Oh, in case you are wondering, I have checked the glass fiter and the debris filter screen and found nothing. I removed the filter screen and see nothing in the sump pump tank where the water pools before being pumped out. Thanks for your help.