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Question DetailsAsked on 6/29/2017

Periodically, a loud sound occurs in my house;

It sounds like a foghorn. It may occur once a day, several times, or none. It does not occur when faucets are turned on or off. It does not occur when toilets are flushed. It does not occur when the AC turns on. It seems to be at random, day or night. I live in a home with an unfinished basement, main floor, upstair floor, and an attic. The sound lasts for a few seconds. The sound seems loudest in the half-bathroom on the main floor. Once when I heard the sound, I ran to the half-bathroom, and the sound was loudest under the sink. When I grabbed the cold water pipe, it was vibrating. I checked the piping in the basement, and the pipes all look fine. Any ideas?

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1 Answer


Likely causes - and start with item 1) below, and I would suspect that half-bath as the source.

1) probably most common - a slightly leaking toilet tank flush valve (look for minor bowl water disturbance from flow coming from under the rim, or if no visible disturbance put some food coloring in the tank and see if it appears in the bowl due to a bit of leakage from the outlet flapper or valve), causing "ghost flushing" - the inlet valve in the tank opening for a very short time to top off the tank after it has drained down a bit - can happen from rarely to quite frequently depending on leakage rate - and the interval will be far from uniform because every time you flush the toilet it refills, so that starts the clock over on how long it takes to drain down enough for the float to open the fill valve.

Test for that other than seeing leakage into the bowl - if you shut off the valve behind the toilet so water can't come in and the noise stops entirely, that was it. Otherwise, when you hear it quickly pull the top off the toilet tank and see if there is disturbance in the water from the fill valve refilling the tank.

If that is the case, stopping the leak solves it - usually the flapper/flush valve, sometimes wiping it and the seat it seals against will solve it, otherwise replacing gasket or the flapper (depending on is the normal solution, though occasionally it is leakage from the seal under the overflow tube assembly. Also, if the water level is too high in the tank so it is wicking into the overflow tube, that can cause the refill cycle - if water is at the top of refill tube after tank fills, lower the float a bit to lower the water level.

You can also sometimes barely push down on the flush lever so just a bit of water comes into the toilet and see if the howling occurs - if so, or if it ever howls at the end of the refill cycle, then your fill valve asembly in the tank may need replacement because the seat or needle valve on the fill assembly is worn. Not a tough DIY job on most toilets, using FluidMaster or similar replacement kits.

2) much rarer, is a pipe leak somewhere in the house piping, causing short bursts of water to come in through a pressure regulator or backflow preventer (normally near where the water comes into the house) which is howling because of a worn seat or just because it is only opening up a touch to make up the pressure loss from the leak.

3) probably even rarer - howling fill valve for reefer ice maker when it opens to fill the ice cube maker tray.

4) probably rarest - TXV valve howl on the A/C - would occur shortly after the A/C turns off, as the pressure in the system equalizes.

5) another pretty rare cause - howling bearing on a fan - would be an automatic one in your case since it happens randomly - maybe a whole house or attic vent fan with bearings going dry - though since the sound is loudest at pipes this is not likely cause in your case.

6) not totally uncommon, though is usually just a flow or gushing sound or a sound like a faucet in another room being opened in normal conditions, is makeup water being released by the pressure regulator on a boiler - but with a worn inlet valve can howl at times. Will occur at random intervals when the boiler needs makeup water due to leakage or air venting - should happen if you drain a slow trickle of water from the hot water/steam heating system (beware - HOT) for a short while (a few to maybe 10-20 seconds) until the pressure in the system drops enough to make it add makeup water.

7) I guess could be a howl in some cases, usually more a loud rushing water sound or a gushing or thump - if overtemp/overpressure valve is opening on a boiler or water heater because it is overheating or pressuring up (which means it needs repair/servicing if this is happening) - would be discharging hot water (typically a cup or few at a time) from the overtemp/overpressure valve drop tube, which may dump onto the floor or go to a floor drain or such. The valve commonly looks like this, coming off the top back or side of the appliance usually -

(the fourth photo in article, showing the water heater T&P valve)

8) howling dump valve on a water softener - when it is recharging the softening chamber, dumping water from it to the drain and refilling with fresh salt water. Should happen, if this is the cause, if you manually trigger the backflush cycle.

9) ditto to rare, but IF you have a recirculating hot water system (where you have basically instant hot water at the taps), if the circulating pump that keeps the hot water circulating in the system has a bad bearing it can howl when it runs (some run constantly, some only intermittently).

10) rare, but some houses have them - if your area (or your home pump/tank system) is at risk of very high pressure (due to being very low on the system, or because you have a high elevation tank or high pressure pump for irrigation or brush/forest firefighting or such, sometimes the regular pressure regulator in the house system is not trusted to protect the piping, so a second one (and sometimes the primary too) are the type which releases excess pressure which might get past the pressure regulator itself, and is plumbed so the excess pressure is released through a relief pipe to a drain or outside. So if your in-house system pressure is getting too high, it could be releasing it in short burst to the drain - would happen typically when no other water use is occurring in the house, as that would release the excess pressure just through use. Commonly looks something like this - first is pressure regulator with pressure relief (opening at bottom is pressure relief port, would be plumbed to drain pipe if expected to operate or if in place where water release would cause damage), second is a pressure relief valve only which would be placed downflow of a pressure regulator:

Sometimes the pressure regulator on a house will be the relief type even if not a high pressure situation - some plumbers prefer that type for general use as it provides a backup in case the pressure regulator malfunctions.

Answered 3 years ago by LCD

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