I tested the water pressure last month and it came up at 89psi. My old pressure regulating valve said it would only go to 75psi and turning the bolt didn't change the pressure, so I assumed it was shot and replaced it. No leaks and the new valve appears to be installed correctly according to the arrows on the housing.
I also removed what I would best call an S-curve in the copper pipe after the pressure regulator and before entering the house. I had googled it and couldn't find anything about why it was there but maybe it acted as an air chamber - not sure. I removed it since it seemed unnecessary and only there to line up the pipes. This then let me put the whole unsightly assembly in a valve box underground. Here's a pic of the before:
Water comes up on the right, into a ball valve, into the pressure regulating valve (PRV), then tees up to the house via ball valve, and down to my yard's irrigation / hose system after a dual check valve. There are pressure vacuum breakers before the sprinklers.
Now, when either the master shower is turned on on the second floor or the hose is run from the end of my irrigation line, the pipes in the opposite end of the house on the first floor (near where the water enters the house) start to vibrate / chatter and make a lot of noise. I have just discovered that the noise seems to be coming from where the main takes a 90-degree elbow and moves into my main shutoff valve and the PRV. Please see the Youtube video of the vibrating here and see it in more of a closeup with a focus on the the vibrating stopping and starting here.
As soon as the master shower stops or the hose is turned off, the vibrating / chattering stops. Sometimes if I open any faucet in the house, even for a second, the vibrating / chattering can stop. These vibrations can't be good, especially for the Sharkbite fittings.
As suggested below, I tried slightly closing the valves, but that didn't seem to do much. I then tried to adjust the pressure bolt on the PRV and it seemed to work for when the hose was on. I tightened the bolt until the vibrating stopped, but then when the irrigation kicked on it starting vibrating again. So, I adjusted it again and this setting only stopped the vibrating when both the hose and irrigation were on. I found something else my experimenting: when I turn off the valve to the house, there is no vibration at all.
I would have to guess that either the new pressure regulator valve or the removal of the S-curve is causing this. I can't tell if this qualifies as water hammer. Does that sound right and how could I stop this from happening? Would I have to re-add the S-curve and remove the valve box? Add an expansion tank? Remove the dual check valve? Better secure the pipes in the wall?
Any help would be greatly appreciated!