[AlwaysHomeNow]

I called the RV parts store around here and they didn't have any check valves in stock. But the tech said that you only need the check valve for winterizing the RV, to keep antifreeze from getting into the heater. He said that we could 'tap out' the valve part and it should work just fine for now. So that's what we did. No more whistle, and we've got the best supply of hot water we've ever had over the 3 years we've lived in our unit.

Thanks again for all your help.