Moaning sound from PRV / pipes

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Pressure Regulator Valve (PRV) and/or connections moaning sound, like a foghorn...

6+ months ago a plumber did the following, all inside the house:

1. replaced leaking line connecting to incoming city water supply line
2. installed 2 new ball shut-off valves
3. installed new Zurn Wilkins PRV set to 45 PSI
4. installed iSpring WGB21B whole-house water filter
5. installed new hybrid water heater, expansion tank, condensate line & pump, etc.
6. installed new kitchen faucet
7. installed new garbage disposal
8. installed new dishwasher

Components, starting with the incoming supply line...

1. Shut-off (ball) valve
2. Pressure regulator
3. Whole-house water filter
4. Shut-off (ball) valve
5. Connected to remainder of plumbing / downstream components

Everything was fine, no issues, no wierd noises or other problems until...

We were leaving on vacation and didn't have the appropriate tool to turn off the water at the street (meter). I tried turning it by hand and with a set of pliers but couldn't turn it off.

So I turned off the 2 shut-offs in the house (see above), put the water heater in vacation mode and we left.

Upon returning, we opened most of the faucets, shower valves, etc. (note we did NOT turn on the outside faucets, washer connection and a few others).

I then slowly turned on the shut-off valve closest to the incoming water supply, followed by the shut-off valve after the water filter. All the faucets seemed to be running fine, toilets seems to be filling fine, etc.

At first everything seemed OK, but in short order we started hearing what I'd call a loud moaning noise that appears to come from the PRV and/or the connections on either side of it.

If I trickle water from a faucet, say up to 1/4 or perhaps 1/2 full flow, I don't hear the noise (or it's low enough I can't hear it from the floor above).

If I open a faucet (cold or hot) all the way, the moaning sound is loud and continues until I reduce the flow or shut it off.

I put a Watts water pressure gauge on an outside faucet pretty far from the PRV, shut-offs, filter, etc. It shows 45 PSI with a peak of around 55-60 PSI, so the pressure after the PRV doesn't seem out of bounds.

I've no idea what the problem is. A few wild guesses on my part:

1. The city water pressure is suddenly much higher. Seems unlikely, but...

2. The PRV is bad. Seems unlikely, as it's pretty new and seems to be controlling the pressure as set.

3. One or more of the filters (there are 2 of them) are clogged and need to be changed

4. There is air somewhere in the lines (note we aren't getting any banging, sputtering, etc.)

5. There is some sort of restriction in the lines

I'm not sure what to do from this point and would be grateful for any suggestions.


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I got the make (Zurn) and model (NR3XL) of the pressure reducing valve and downloaded the documentation from the manufacturers web it. It was fairly thorough, with installation, maintenance and troubleshooting info.

The troubleshooting section included some suggestions if the unit is making noise. One of them was to temporarily increase the pressure setting (loosen the locknut and turn the adjustment screw clockwise) and see if the noise goes away. There was no mention of how far to turn the adjustment screw.

I turned the screw clockwise about 90 degrees and turned on various faucets, showers, etc. and the noise was gone.

I checked the water pressure gauge (which was still attached to one of the outdoor faucets) and the pressure increase seemed negligible, perhaps 2 to 3 PSI.

I then turned the screw back about 90 degrees to about where it was set previously and retested. Again, no noise! So I tightened the locknut and declared victory, or at least a temporary truce.

I don't know if some debris had gotten stuck in the unit and moving the adjustment screw let it clear out, or something re-seated...

I don't like not understanding what the problem was and why turning the adjustment screw fixed it, but for the time being it seems we are good to go.
Hey, wait a minute.

This is awkward, but...

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