Hi guys, quite puzzeled right now. Today woke up early in the morning to a terrible constant pipe banging sounds coming from the pipe leading to the irrigation valves. The sound was quite audible from outside where the backflow preventer is. The backflow preventer was leaking a lot water from the top. This was all happening while the sprinkler system was running. I had to close the valve feeding the system from inside the home to stop the banging. What could be the cause of this? The backflow preventer seems to be quite similar to this https://i.ebayimg.com/images/g/QZEAAMXQU6tQ~gRM/s-l300.jpg Thanks!