Red said when you turn on the pump, the pump starts and builds up pressure then shuts off. Then, when you go to use the water, the pressure drop causes the pump to kick on again to get back to the desired pressure level.
I don't know if this makes a difference either, but when you hook a water connection hose to most RVs, you do not turn on the pump. You just use the pump to pull off your water tanks only.
Yep, pressure loss. If you have a fitting leak somewhere or a check valve at the pump letting the pressurized system backflow into the reservoir then the pump will chirp or cycle for a second to bring the pressure back up. This is not like an irrigation booster pump where there is actually an electrical signal from the user to kick on the pump.