ocs,

Yes. First, what is your water operating pressure for your system? Did you mean to say your irrigation system takeoff is before your pressure regulator in your house/garage? Aloha

The pressure of my house is separate from my sprinklers. They come directly off the city in our street. But on another note, A different plumber that works with sprinklers said it might be a result of a wire from the control to the valve being damaged and not making a clear connection. So that's next...

ocs,
Check your street pressure which will be high. It may be too high for your system (banging pipes). The velocity might be too high in your pipes that when your valves close they get hammered by the water stopping at the shut valve. Just a thought. Check your pressure or ask your water company, they will know your street pressure. High pressure can wreak all sorts of havoc with your system. Always good to have a plumber friend. See if he can take a look and check the pressure for you. Aloha

I vote for the high pressure + velocity theory if a solenoid is what is stopping the flow leading to water hammer. Solenoids close pretty fast, one way to eliminate a high velocity/pressure hammer is with an actuated ball valve (not a cheap option) though I think they may be making a solenoid that closes more slowly than a run of the mill soenoid. Another option would be to drop the line pressure just upstream of the slapping solenoid by installing a pressure regulator. Curious to know what your pressure is.

You should be able to get a setup consisting of a 0-200 psi gauge connected to a female hose thread fitting that can be simply screwed onto a hose bib to check pressure; if not, make one yourself.