Banging pipe

[Marlonc497]

Hello, today I was woken up to a loud pipe banging sound originating from the irrigation pipe. Once I got outside I observed the backflow preventer shaking and expelling water continuously. This issue occurred as soon as the irrigation system was scheduled to come on (2am). This is a problem I've been combating with for quite some time. It is very hard to replicate during the day but seems to happen pretty reliably during the night. I've already replaced the backflow preventer and installed a water hammer arrestor but no dice. Last year I seemed to have somewhat fixed that problem by partially closing the outlet valve of the backflow preventer in order to restrict water flow to a certain degree. Not sure if it was luck though. Despite this I would like to fix the root of the problem.

Backflow preventer for reference: https://www.homedepot.com/p/Apollo-...A2F/307723093?source=shoppingads&locale=en-US

Thanks!
Marlon