Maybe I overreacted a bit there<g>
Do you have an automatic sprinkler system in your lawn?
If so, maybe there's a broken pipe, and you don't think it's turning on because no water is coming from the sprinklers.
Also, I often hear water running from a different location than is actually drawing the water. The noise travels very well through pipe, and sometimes just reaches a sort of sound chamber, where you will hear it more loudly, even though it's coming from a different location.
I had my property blue staked, because I needed to plant some trees. I was hoping the water guy would have marked my yard, but he was quick to shoot the street and leave. Two blue arrows that pointed to the meter boxes - Um, WELL DUH!
I don't know if I'll ever figure this mystery out, but I'll keep trying. It doesn't happen much anymore. Maybe it's just coincidence that it only happens when the neighbor's daughter is there. I surely don't want to start a neighbor war, and I'll shut up until I have facts.
And BTW - I was wrong about one of the sheds being over the property line. The other one is, but it doesn't bother me, and I took the free advice of a surveyor (wow - I'm in the wrong business $$$) and judged by where the water and gas lines were. The space between may be considered an easement. As long as I can put my wall up and block their noise I'll be fine. (Yes - these are the "drunk singers" I've mentioned before.)
__________________ "Aw! Why does everything that only happens to stupid people happens to me?" - Homer J. Simpson