No idea about your trailer, but stripit is correct--you should be able to locate the pump while it is running by the noise. Fifth wheels I have seen have the pump behind the access panels in the basement area, or in the kitchen area under the sink. If it is running, but no water is being pumped, that is strange--has to be out of water, or lost its prime. Most of the pumps are self-priming--if the suction is covered by water, it will suck the water up, and pump water somewhere until the faucet is closed. When pressure builds in the system, the pump shuts off. Intermittent pump noise indicates a leak somewhere, but if no water is moving while the pump is running, I vote for a bad pressure sensor in the pump.
Do you get water when the pump is running? And it just keeps running when you close the faucet?
Another idea--there may be a winterizing bypass kit installed. You will need to check all the valves in the lines behind the water heater for correct flow direction. Perhaps the valve in the suction line for picking up antifreeze is open?
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired