adp4501/5?

Hi
Anyone help, my dishwasher fills up then when the water should be 'sprayed' around the dishes a continuous hum can be heard and water just trickles out of the arms, when the door is opened then closed again it works for a few seconds then back to the humming, it sounds like the pump is trying to work but just can't, does this problem sound like any other people have experienced and if so how was it rectified.
Many thanks