Pipes knocking around 120bpm

I have a very odd issue that I can’t solve, perhaps someone here could help. The pipe attached to my main shutoff valve is emitting a soft knocking sound at around 120 beats per minute. The sound persists as long as there is any amount of pressure, and I can feel it in the pipe nearby as well as in the valve handle itself. The weird part is that if I turn on any hot water tap, the noise vanishes. I’m a new homeowner so I don’t have much experience, so any help would be appreciated. What I’ve checked so far:

Drained the system completely and refilled

Turned the water off overnight and checked toilets for leaks

I don’t feel the pulse at the water meter line

Turning hot water on anywhere in the house stops the noise.

Thanks in advance!

Waldowal ,
@Waldowal@lemmy.world avatar

Might be caused by sediment in your hot water heater (assuming you are using a tank water heater). If you’re not familiar, there are tons of articles out there on how to clean it out.

A secondary concern is that you seem to have hot water moving through the system when you don’t expect it. Do you have any water circulators on the house on faucets (so you get instant hot water at faucets?). That could explain it. Otherwise, you might have a leak somewhere.

Ludrol ,
@Ludrol@szmer.info avatar

I think it could be a turbulence inside the pipes that resonates with the pipes and causes the knocking. You could try to fix the pipe to some wall.

ttenborough ,

Do you have a PRV? Is the sound worse at the PRV?

The hot water flow making the sound go away isn’t explained by a bad PRV but everything else could be.

h0rnman OP ,

PRV? Not sure what that is or where i would find it

nowwhatnapster ,

Pressure reducing valve. Typically found directly after the water meter to reduce high municipal water pressure to reasonable residential water pressures.

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