SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I live in a neighborhood in Houston, TX and share a meter box with my neighbor, although we have separate meters. In 1989 the neighbor's son decided to try being a sprinkler installer and put in his first system in my neighbors yard. I do not believe he put in a backflow preventer, as required. The house has been sold several times since that time. Whenever their sprinkler system runs, I get a loud constant noise in the pipes in my attic. It is especially loud when it starts, and when it changes zones, but it is a constant vibrating noise in my pipes. It literally sounds like a small generator running in my attic. I have asked numerous plumbers over the years, and called into radio shows, with no effective solution.
If I turn off the water valve to my house, the noise stops, so the noise is not traveling in the pipe itself, but in the water in the pipe. I have had the water meter changed twice, and have reset the air chamber a hundred times, with no change. I have dug up my water line to make sure it doesn't contact my neighbors. I was wondering if an in-line check valve may help? And ideas on what is causing this?