phantom water leak

ok, I have a very odd leak situation. I was out of town and a few days ago my wife noticed an unusual noise in the bsmt when I was gone- the sound of water running (there's just the two of us) when the washer/toilet/DW, etc were not on. It basically sounds like someone is taking a shower when no one is and there is no water running (intentionally)

From the water meter I can confirm flow of almost 1 GPM.

The toilets are NOT leaking. I've looked in the toilet tanks, nothing happening, and also shut them off and I can still hear the sound of water running in the basement (copper tubing supply is overhead, unfinished ceiling). The noise is loudest in the tubing at the front of the house where the water line enters; it's much lower at the other side of the house at the far end of the supply. If I shut off the water at the meter the water flow sound in the bsmt stops (of course) and the dial on the meter doesn't spin; it otherwise spins when there is nothing on/open in the house. There is no master shut off inside the house. I have shut off water to the dish washer, etc, and still hear water running when in the bsmt. There is nothing with a drain (water heater, etc) that could have a leak spraying directly into a drain.

So, since I have no puddles in the bsmt, I assume there is a leak between the meter and the house (100+ ft). Yet, there are no damp spots in the lawn and it is very dry right now so I would assume it would show up as a damp spot after 5+ days of a leak this size. I am in TN so I assume the line is not burried very deep underground

If there was a leak between the meter and the house it would seem that it would not be so severe and that I would not hear it so obviously in the house. Or would I hear it so obviously? I see/feel no damp spots on the lawn between the meter and the house. I have two outside spigots and neither are leaking.

Ideas? I know this is simple but I am stumped.

I assume I have a 3/4 supply line to the house. Is this something that a pro can shut off at the meter, dig up, break into the pipe and run a camera up it to see if there is a break?

Do you have a sprinkler system to water the lawn or anything like that? What about the water heater relief valve (where does it go)? Some homes will have a trap primer to keep the trap in the floor drains filled (usually just a drip or a trickle when something is used). These can sometimes fail and run when they are not supposed to, but this would be a much smaller flow than what you are seeing. Do you have other systems that may use water (water softener, humidifier, etc.)?

If you had a shutoff in the house, I would turn it off to see if the meter still runs. If it does, the problem is between the meter and the house. If it stops, the problem is in the house.

I would probably add a shutoff in the house. That would help to figure out where the problem is and it is sure nice to have a shutoff inside in case of emergency. If you have a pro install the shutoff, he can also help you find where the water is going while he is there.

Ok, yesterday I did add a shutoff inside the house just to be 99.999% sure the leak is outside. It is outside. The leak detector guy came this morning and found it and of course after digging it up it is right where he said. There is a crack in the copper tubing right where it enters thru the block.

My next question is the "proper" way to replace this so I will start another thread on that.

edit: to add some more info on this, I called a local plumber and they could not help on locating the leak but gave me the number for American Leak Detectors (or similar). They came out and first did a test pushing a rod in the ground and listening thru it with a set of headphones. Didn't work. Next they tried to locate the line but since it was plastic, no luck there. Finally, they disconnected the water line at the meter, hooked up helium to the water line, and "sniffed" around for the leak. Found it no problem.