It sounds like you may have a small leak at one of the lines or fittings. Maybe kitchen faucet etc. Look under all the cabinets and water heater area. It's good to use at least a cheap pressure regulator on the supply faucet. If connected to city water, I would always shut the supply faucet off if leaving for awhile and at night. If running off the fresh tank I also keep the pump switch off if leaving and at night.
RV's are known for cheesy connections and water leaks. IF, when using your water pump, you hear it randomly kick on for a second or two, and you have not turned any faucets on, it sometimes means that you have a small leak and the pump pressure is bleeding off causing the pump to turn on.
You may use that as somewhat of a diagnostic tool. Have water in the fresh tank, disconnect from the city water, run the water pump and open all faucets enough to get any air out, then let it sit with the pump switch still on and listen for the pump to kick on. It may take quit awhile if its just a drip.
I had this issue with a drip at the water heater under the bed. If you dont recognize whats going on, you can end up with much damage.
