Water Pump Issues

You might try switching the pump over to the winterizing line and placing it in a 3 gallon pail of water. See if that gets it primed and it stops pumping air and gets quieter. If not its probably necessary to remove the pump and see if there is anything rattling around in there. 

Actually, it would not be difficult to replace. The fittings on mine which include the lines and the strainer all screw on to the input and output side of the pump. The hardest part is splicing the wires and even that is not difficult.I know that from when I removed mine to disassemble and reassemble. Even that part wasn't too difficult if one has the proper bits for the machine screws.

Well, learning something is good. Going through the whole process to find out it was something very simple isn't so good, but this is something that may benefit someone else down the road. I'm glad you did not have to go buy a new water pump only to find out it did not fix the problem.

The city water connection is on the high pressure side of your pump. There is a check valve to keep city water from leaking backward through the pump into the fresh water tank, and another one keeping the water pressurized by your pump from leaking backward out the city water line. There is no reason for the city water connection to cause your issue unless there is water leaking back out of the city connection when you turn on the pump. I think your problem lies elsewhere, either on the suction side of the pump from your fresh water tank or in the pump itself. If using the antifreeze suction line from a water container doesn't fix the problem then its most likely the pump.