two years ago our workspace was converted to a living space, and recently we realized there were several issues with the plumbing. (I posted something earlier, but couldn't work out how to post pix.) At that time the problem was with two 40 gal water heaters above the shower. But another problem has taken precedence. When the hot water is turned on, the hot water pipe in the bathroom starts vibrating and humming loudly. If the water is turned on (hot or cold, usually) in the kitchen or for the bathtub, the bathroom sink hot water turns on, to a dribble, and the noise begins. It would also just start up spontaneously. If we turn off the hot water valve under the bathroom sink, the noise stops.

The plumbers (who did the original work, but they are charging anyway) have been here 3 times. The first time, they took apart the shower control, maintaining that was usually the problem. The second time, they fixed the problem the first man created. This time they put an anti-knock valve on the hot and cold supply pipes for the bathroom and kitchen sinks, and installed quarter-turn valves on the bathroom sink water supply. Everything seemed ok, except when I turned on the bathtub hot water, the knocking started again, and the hot water in the sink started dribbling. I could kick myself for not turning on the bath while they were here, but I took their word it was fixed.

what should we have someone look at next...and could rust debris in the hot water supply he part of the cause?

Air in the lines and or a rubber washer on the end of a valve stem can cause vibrations.

srloren

Thank you for the suggestion. The valve was changed yesterday to a quarter turn valve, so I would think that isn’t the problem. However I do want to clarify something in my mind.

Yesterday, the plumbers installed Anti-hammer arresters on the bathroom and kitchen water lines. But in looking up anti-knock arrestors, it appears to me that they are used to stop hammering after water is turned off abruptly. Our problem is that when water is turned on in the bath tub or kitchen sink, The hot water in the bathroom sink actually turns on (to a dribble), and starts humming loudly. At other times, even if we are not using water, it just turns on by itself and starts humming. As I stated earlier, the plumbers have been here several times, and done various things, including the anti-Knock arrester, none of which have been effective. What I am wondering is whether antiknock arrestors actually had any hope of fixing the problem, or are these guys just doing various things that actually aren’t addressing the problem at all.

If it's a 2 or 3 handle faucet, it's probably a loose washer. If it's single faucet, replace the cartridge.

either rebuild or replace the bathroom sink faucet


IT 'probably' has a loose washer or an 'ailing' cartridge

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

the 'anti knock' arrestors will not cure the problem.
there is a loose washer somewhere in the system.
nothing external will cure that.
find it and repair/replace it.