Water pump cycle w/o using water.............leak of some sort
Small leaks are hard to find visually....lay couple sheets of TP down around any suspect source to check for small drips
Suspects:
Toilet water valve leaking thru or dripping at connection (hard to see)
Connections on any fittings......faucets, showers, backside of water heater
City water check valve dripping
Water heater drain plug
Water heater T&P Relief Valve weeping
Low point drain valves
Pump internal check valve leaking back into fresh water tank
You have a small leak.......some where. The hunt begins.....find it before water damage to floor/wall