Well we got to the bottom of it today. I couldn't see this with the oil in the tank but for some reason schindler used a long hose on the discharge side of the valve that went all the way down into the tank and stopped just above the pump, but at some point came loose and was getting sucked up against the pump screen causing the pump to cavitate. The only odd thing was why it would do it intermittently, but we re adjusted the hose and refastened it and we couldn't get it to repeat so I think it's solved.
