I have a shallow well single pipe jet pump with 20-40 tank. Pumps starts on its own every 20-30 minutes as pressure drops without any water use, no tap drips or leaks that I can detect. Shutting supply valve to house stops problem so I tdon't think it is the foot valve. Tank pressure remains at 20 with no water in it once removed. What else can I check? Can outside frostfree taps cause this problem overtime? Can water leak into toilet bowls without it being noticeable and without triggering a refill of the toilet tank, which might explain gradual water pressure drops and the restarts of pump?