I have almost the exact same problem.
I do not have a pressure regulator on the house itself, The Sprinklers are T-ed off the mainline before it even enters the house.
The sound is very faint, but it is distinct. It sounds like a rythmic waterhammer. The whole time the sprinklers are running, I can hear a faint bump, bump, bump, bump,....
How can I be hearing anything at all inside the house if no water is running through the house plumbing? The valves do not seem to be chattering, and it happens whenever any of the zones is energized, so it is not one valve.
The system is brand new, all Hunter parts from Sprinkler warehouse, in fact it is not quite finished yet, The electric is not hooked up yet, valves are turned on manually at the solenoid. But sod is down, and it needs to be watered.