Intake to Rinnai Vibrates Intermittently

[dabash]

Hi,

I live in an 11-year old house in MA, and over the past week the cold water intake to our Rinnai tankless heater has been vibrating on and off. Sometimes when we're using hot water - dishwasher or laundry - but also other times when everyone's in bed and nothing's running, hot or cold.

I flushed the unit because it was almost due for it anyway but it didn't address the issue. When the pipes start vibrating, closing the laundry room valve if the machine's not running can help to tamp it down. Last night the vibrations made their way up to the primary bedroom toilet and I had to close that off to stop the noise.

We do not have an expansion tank, and we haven't done any work on the house that would have impacted things. Any advice on how to address this would be greatly appreciate - thank you!

NOTE: Video won't upload, so here's a link.

 

[Fitter30]

Have a pressure reducing valve? Thinking some solenoid valve or toilet is barely leaking through. Prv with little flow might be going bad.

 

[Sponsor]

 

[dabash]

Have a pressure reducing valve? Thinking some solenoid valve or toilet is barely leaking through. Prv with little flow might be going bad.

EDIT: I traced all the copper and PEX, and I don't see a pressure reducing valve. Also, we haven't had the vibration / noise issue in 24 hours, despite doing laundry / dishwasher / etc.