Pump runs but there's no demand

We have a 150' well with a submersible pump. Occasionally the pump runs when there's no water running anywhere on the system. After much head-scratching I've come to the conclusion that there must be a check valve down inside the well, and that the pressure tank is forcing some water back thru the check valve, causing the pump to refill the tank. There are definitely no leaks or dripping faucets anywhere in the house, and the line from the well is 1" soft copper that I installed about 2 years ago with no leaks observed before the trench was filled.

Any other possibilities I should consider? I've never had the pump pulled and don't know how long it's been down there, but it's probably been many years.

Pull the well cap off and look down and see / hear any water spraying or running. Do you have any idea how often it cycles? Do you have a pressure gauge you can watch and see the pressure falling? Have you put dye in the toilet tanks to see if they are leaking slowly.

you can pump the system to a high pressure and shut off a valve [install it if need be] at the tank inlet so that you isolate the well side from the house side before digging or pulling pipe. If the pump cycles with the well side shut off then you have your leak downstream somewhere.

I don't like valves between a sub pump and its pressure switch..

So I suggest shuting off the water past the pressure tank and watch the pressure guage. If the pressure falls, the leak is on the well side. If not, then it's on the house side.