Don & Barb;
It sounds as if it is drawing air some place. I would suggest you check all your connections on your suction line from the tank to the pump. It would seem to me that if the pump it self were sucking air, water would leak out when it shuts down.
I am not speaking from experience as I have never had a problem with my pump. Maybe someone will pop in here with their thoughts.
Don & Bev Morgan Weyauwega WI, 05 Itasca Horizon 40KD, 400 HP Cummins, Adopted by a great couple, Toad 07 Saturn Vue AWD, Air Force One, TST 510 TPMS, Mayor of Weyauwega 2007 - 2013, Waupaca Co Board Supervisor 2010 - 2014