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The mystery noise might not be plumbing. Could be a drain pipe rubbing somewhere too. Figure out where your drain lines are, run cold, than hot. If you get some expansion ticking, it could be that pipe cools during the night rather slowly causing the noise.
cold:long enough to make the drain pipe temp cool off.
hot: listen closely. If it's the drain pipe, you'll hear it fairly quickly.
sigpic3:00, I mean 5:00, and work is done. Time to crack a cold one.
There are no drain pipes in the vicinity of the noise. And I typically hear it several hours after we have gone to bed, so nothing should be flowing in the drain pipes anyway.
Nope. No recycling pump. And no hot water lines near where the noise is coming from.
Unless I am wrong about where the noise is originating, the only things in that area are the incoming water supply line with its shutoff value and PRV. A single flexible duct supplying air to one register in the bedroom. The electric wires feeding a couple of outlets in the bedroom and a single bulb in the crawl space. And some type of control box that is wired in near the crawl space fixture and has a very narrow gauge wire running off toward the other side of the house (I haven't traced it yet so I'm not sure what it is).
One more comment: The thing that I find really strange about this is how regular the tapping sound is. It is kind of a dull rap like tapping your knuckle on the desktop. It is louder sometimes and software at others, but it is ALWAYS tapping at once per second. The frequency never changes - it is like a metronome. At first I thought it had to be something swinging like a pedulum and bumping against another object, because everything else (like pipes rubbing due to thermal expansion) should be more random.
I even considered the possibility that I had a mouse running along the electric lines or pipes causing them to bounce up and down and hit the joists, so I put down poison and added hangers in the places where the pipes or wires had not been attached to a joist. It didn't help.
Had a customer once with the same type of problem and because it was so intermittent, everytime I showed up at the house it would not produce itself. Finally discovered that it was a noise resonating from the city's water system. I could actually feel the tapping at the water meter. Ok, someone might get mad but you have one flush on every toilet, shut your main water supply off just for one night and see what you think.
I'd still check this. Depending on the type of PRV or if it's failed in some way, the water can "bounce" off the expansion tank opening and closing the checks causing clicks.
That sounds like a good explanation, but I'm getting in over my head here. My water meter is all the way down at the street, so where would the check valve be located? I don't think there is anything in the crawl space before the main shutoff valve except the two connections to the outdoor hosebibs.
Or is this just a case of "call a plumber and ask him to check it"?
I would check the PRV first by installing a pressure gauge on a hosebib, they have ones that will monitor your pressure and "remeber" the highest pressure encoutnered, by putting one of these on you can make sure your PRV isnt leaking by building up pressure too much.
I finally bought a gauge to measure the pressure at a hosebib. At 7pm last time the initial reading was 90 psi. I left it on overnight, and the current reading is still 90 psi, but the maximum is 110 psi. So at some point during the night the pressure was significantly higher.
OK. I finally just took a book and sat in the crawl until I heard tapping. Then I put my ear against the PRV, and I heard a clear "squish - tap - squish - tap" that was at the right frequency. It didn't seem very loud in the crawl space but my wife could hear tapping up in the bedroom at the same time. So this must be it.
Am I right that the next step is to replace the PRV? And is there anything else I should have the plumber do at the same time? Like install a pressure gauge? ...