Yep, that was the one with the brand new valve diapragm. For kicks, and mainly to see if I could cap the existing pop ups, I pulled one of them off and ran it. There was no noise, obviously that wouldn't work, but free flowing there was no thumping.
There is one more valve that I didn't know about, a pressure reduction device after the water meter. I picked up a water pressure gauge, our water pressure read 100-110 PSI.
So, went to adjust that, and guess what, it won't change, won't adjust up or down. I adjusted the main line shutoff before the water meter and pressure reducer, pressure is still 110 PSI but the thumping is gone from all systems (for now)
I'm not sure if I own the pressure reduction device or if Denver water does. When I figure that out I'll be fixing/replacing it or having Denver Water help out with that. . . Then I will re-open the main line shutoff back to wide open, and see if it is the pressure reduction device.
With the main shutoff partially closed the pressure is still high (110) the flow rate seems adequate, no pulsating pop ups and they are watering correctly.
More to come, and hopefully this will be solved!