My home is above ground and the water lines are galvanized pipe. I can hear water running through the pipes like a faucet or sprinkler is on outside. There is no standing water or water under my house. Could it be a broken pipe underground?

If the pipe broken BEFORE it enters your house... you won't hear it. And I haven't seen any cases where a water pipe LEAVES the house and goes underground. But if you have an out building that has water to it... or a lawn sprinkler system then that is a possibility. THough its typical to shut the water off to them and drain them for the winter season where the weather gets that cold.

Are you sure your toilets aren't leaking? I'd make a note of your water meter when you leave for the day... and write down the numbers again after you return home...

How bad is it? Is it continuous? How long have you been hearing it? Could be just the toilet tank refilling itself.

Have you checked the little pointer on the water meter or the pumps gage for any movement on the pointer or a drop in pressure after the pump shuts down. Let me know, Tom