Moaning sound from kitchen plumbing (1 Viewer)

[JohnVee]

So the pipes in my parents house give a groaning or moaning sound ONLY after turning off the sink faucets in the kitchen. No other sinks, washers, hose bibs, or toilets cause this. It does not happen while the water is running but will start about 10-20 seconds after turning it off - it continues for 2-5 seconds The dishwasher is fed by a line from the sink; using the dishwasher will not cause the noise.

All of what I'm finding relating to causes stemming from a sink, and the general fixes, are about the noise happening while the faucet is running. I can run it for an hour and it will only happen once turned off. Hot or Cold or Mix makes no difference.

Drain and vent lines are PVC. Supply lines are CPVC. The house is 13 years old. The sink faucet is 10. There are plenty of other noises in the pipes that can be heard in the ceiling of the finished basement but this one is only noticeable in the kitchen.

Whaddya y'all think? Water pressure and various faucet washers are the commonly mentioned culprits for noise while water is flowing. I've found nothing for when it's not. Thanks in advance for any help on this.

EDIT: I'd suspect water hammer, but that's always been a banging noise where I've encountered it, not a moan.

 

[Music Man]

Try pouring a bucket of water in the sink and see if it still moans.

 

[1911]

Their kitchen sink is haunted?

 

[JohnVee]

Try pouring a bucket of water in the sink and see if it still moans.

Good call. Yes, it did moan. Funny, though, how we've never heard it happen through hundreds of dishwasher cycles (dishwasher drains into the garbage disposal...same drain I poured water into). So now I'm not dealing with a faucet or a washer. There is a PVC vent line inside the island that terminates into a vented cap just below the countertop. I'm guessing that's where I'll find the problem. I feel it vibrate during the moaning noise but I feel all parts of the system doing the same. Every damn bit of the system is glued together, so I'm hoping to stumble into an easy fix before I crawl in there with a saw, glue, and parts.

 

[JohnVee]

Their kitchen sink is haunted?

No, they're the original owners of the house. Possessed, maybe?

 

[micruz60]

Probably the pressure vent in the island, doing it's best.
From a matriarchal family of plumbers..... and I slept next to a holidayexpress once.

 

[thebus]

Seems like you need to replace the air admittance valve. Pictures help