If the water shuts off and the bowl retains water to cover the valve, I'd just get used to the noise. If you turn off city water and the water pump for a night, and the next morning the bowl still retains water, I think you're O.K.
If water continued to run, I'd think a bit of construction debris was caught in the water valve, but you say it does stop, so I don't think it's an issue. Most all RV toilets do have a screen in the water inlet to prevent valve malfunction, you could take water line off and clean the screen, see if that makes a difference.