Raise bed drip irrigation water hammer problem

I have three raised beds which use 1/2” supply tubing headers and 1/4” drip tubing off that. Water is supplied by a single Orbit irrigation timer. At the outlet of the timer is a 25 psig pressure regulator. The total flow should be about 2.2 gpm based on the number of emitters in the tubing. This worked fine for a while, but now I’m getting water hammer. No hammer occurs without the timer. Swapped the timer with another one I had and it seemed to eliminate the problem briefly, but the hammer returned. Tried new regulator but that didn’t help.

Thoughts on how to solve the issue?