[whatsthissound]

Link to listen to mystery sound


We are experiencing a banging sound in our home and cannot identify it. The water heater was recently replaced before this sound started happening, and we are suspicious it is somehow related (though it may be innocent). An expansion tank was also added to the cold water line supplying the new water heater (no expansion tank previously). The sounds have been happening for the past 3 months, but otherwise never ever happened in the past 34 years in this house.

There are anywhere from 1 to 4 bangs. They vary in volume and rhythm. It seems to come from the basement, but can be heard and physically felt all the way on the 2nd floor. We have placed a recorder on top of the water heater to capture the sound when it happens.

It does not happen when turning a faucet on/off, flushing toilet, or other things that draw water. We can't MAKE it happen. It usually happens late at night or early morning, strangely most often on Mondays and Saturdays. It happens when everyone is in bed, or when we're all sitting together watching TV or something, and it happens when no one is home (found when reviewing the recording later). Sometimes it happens twice on the same day, sometimes it happens on 2-3 consecutive days, sometimes a week or more elapse with NO banging sound (that we hear, at least).

A hiss seems to start building up before the banging happens (audible on clear recordings when the basement is quiet).

The plumber who installed the hot water heater doesn't know what it is. We can't make it happen on demand, but have played the recordings for him. He says it doesn't sound like water hammer and sounds more mechanical. But the banging sound happens when the A/C, washer, dryer, dehumidifier, humidifier are all off.

It's driving us crazy and is worrying.


3 of the clearest recordings (with the hiss building up before the bangs) can be heard here: https://soundcloud.com/user831801226



Does anyone recognize this sound and its irregular behavior? What is it? How do you fix it?

Thank you for any ideas you may have!

[hkstroud]

Don't know what it is but I have heard it before. It is some kind of pump. A piston type pump that takes only 1, 2 or 3 strokes to restore a pressure or level. I could be a liquid or air pump, electrical powered.

[hkstroud]

Do you have an airless paint sprayer?

[whatsthissound]

Thank you for that suggestion. It's good to know someone else has heard this before! No, no airless paint sprayer. The basement has A/C, furnace (with humidifier), water heater, washer, dryer, freezer, sump pump, dehumidifier. The banging sound has happened when various combinations of those things have been running, but it also has happened when NONE of those things was running (no freezer hum, no A/C blowing, no sump pump emptying, no laundry, no water running on the recording). The humidifier is turned off and the water to it is turned off. The dehumidifier has been turned off to rule it out as a source. We dumped buckets and buckets of water in the sump pit to make it pump but couldn't cause any banging sound there.

In addition to the water heater being replaced, the A/C got its annual service (inside and outside) a little before this sound started happening.

[hkstroud]

Certainly sounds like an airless paint sprayer to me.
Certainly has to be electric. Might try turning breakers off one at a time for a period of time to see if any thing changes.

[talaniman]

What is your house water pressure, both before and after the pressure reducer valve? What is the expansion tank pressure setting? Was it preset or adjusted after installation? It certainly sound to me like you have an imbalance in your pressure settings, possibly, and the first course of action in such cases, without knowing your system and it's specs, is to check it, and analyze the results for the proper adjustments, or related problem if there is any.

It's also possible the changes to your system recently will take some getting use to, but you cannot say without making and noting what the pressures are and if they are within spec. Pictures would be nice, pictures and model numbers would be better. I have to agree with HK though that the noise is from your system in some way, but from where, and what, takes more data to pin it down.

Look forward to MORE information and your recordings were great.

[whatsthissound]

talaniman -

Unfortunately I don't have pressure measurements for you - and those are probably the most important thing! The plumber who installed the water heater said he could come back and take those readings. The front exterior faucet seems to be before the pressure reducer, so maybe we could measure there and at the basement faucet after the pressure reducer ourselves, if we get a pressure gauge. I'll have to ask the plumber about the expansion tank pressure setting being preset or adjusted, as well. The expansion tank says "Precharge: 40 PSIG" on it.

Expansion tank: Amtrol T-5
Water heater: Rheem PROG50-38N RH58

The documentation for the expansion tank shows that it is the right size for a 50 gallon tank.

The water heater is set at the recommended temperature setting of "triangle"

Photos of the setup are HERE

One thing to note in the photos, the hot water pipe flowing out of the water heater seems to have been unfastened from the joist in order to swap the water heaters. That pipe used to be flush against the joist and fastened there with that metal strap, which was why a chunk of foam pipe insulation had to be cut out to fit. Now, the pipe isn't fastened to that joist and there is a space between them. When we noticed that, we twisted the foam pipe insulation to pad the new space between the pipe and joist (leaving the strap still unattached to the joist), but it hasn't changed the sound. It may be unrelated, but it is a change from the prior setup.

So the only changes have been:
1. remove 40 gallon water heater, replace with 50 gallon water heater
2. add expansion tank
3. pipe is no longer secured against joist
4. horrible banging sounds started happening randomly
5. the air conditioner also received its yearly routine service prior to the banging sound starting

[talaniman]

The only pressure measurements you need is AFTER the pressure reducer valve (House System Pressure), and the Expansion Tank AIR pressure. They should be pretty close, and a simple task to add air to the tank if needed, or adjust the PR valve. (The outside faucet is the city delivery pressure)

This is covered in the installation instruction you supplied by the way (Pretty standard industry wide). With tank empty of water, adjust air precharge to match cold watersupply pressure. Besides this simple adjustment your plumber did an excellent installation, so I think the hissing is the pressure relief valve, and the knocking is an undercharged expansion tank doing its thing when water usage is really low.

Please let me know what you find and what was done about it, but a pressure check is where to start.

[hkstroud]

Aaaaaaaaaaaaaaaa

[hkstroud]

You can check water pressure with pressure gauge ($15-20) shown below. To check pressure coming from street, attach to exterior hose bib. To check pressure after pressure reducing valve, attach to water heater drain valve.

If you get the version shown (with red needle) and leave attach to the water drain valve if will record any spikes in water pressure that the water heater might experience.

Do you ever see any signs of water from the pressure relief valve?

[whatsthissound]

Is the water heater drain valve the best place to test the water pressure post-pressure-reducing-valve? Would a basement faucet work just as well, or is directly on the water heater better because it's closer to the action?

So if for some reason the air pressure in the expansion tank did not match the house system pressure, and they were adjusted to match, would you anticipate the sound stopping? Does a normally functioning expansion tank with proper pressure operate fairly quietly?

The water heater flue DOES touch the gas line piping, and we were concerned about that. They are so close that you cannot slide a piece of paper between them. I would swear that they did not touch with the old water heater, but the plumber says they did. We were worried about the intensely hot flue touching the pipe full of gas, but the plumber said the gas line is cast iron and the heat wouldn't be a problem. The city inspector didn't have a problem with it either, even when it was pointed out to him. Is this dangerous? Or is it a possible source of noise, from the flue expanding/bending around the gas pipe as the flue heats up? (…though the banging doesn't happen every time the water heater heats). We're uncomfortable with it and might have to have the flue adjusted away from the gas line just to feel better about it.



The water heater flue does NOT seem able to touch the cold water pipe. There is about 1/4” between them.



There hasn't been any sign of water on the floor released from the pressure relief valve, but we will keep an eye on that.

Thank you both for all of your replies!

[massplumber2008]

Sounds like the AC SYSTEM or humidifier in stuck position to me... about the only things that can cycle and make noise like that.

Also, the expansion tank needs to be hung better there. Here, if the expansion tank diaphragm were to rupture 4-5 gallons of water will flood the tank and instantly add 35-45 LBS to that press type copper fitting under the tank... could very well bust that elbow off and flood the place!

I'd shut the AC system and make sure electricity is shut off to the humidifier for awhile and see if all goes quiet. If all goes quiet, have AC guys come back and go through the system again!

Finally, I've seen all kinds of pipes touching pipes...never heard these sounds so doubt that is the sound heard here. With that being said. The plumbers poor response of, "it was that way before" is pretty weak. I'll bet a local plumbing inspector wouldn't be too happy to hear about that response..UGH!

Mark

[whatsthissound]

Mark -

What could be done better regarding the expansion tank? As awful as the banging sound is, a flood would be worse. If the plumber ends up coming out to test pressures or fix the expansion tank charge or rework the flue, we should insist that any modifications that need done to the expansion tank setup be done then, too. Frankly, if it could be done better and safer, that alone is reason to have him (or another plumber) come.

The city inspector was fine with everything as pictured in the photos (expansion tank setup / fittings, pipes touching). It's a concern to hear there could be a problem with the expansion tank setup that both the plumber and inspector didn't see as a problem.

Could it be the AC when the sound happens whether the AC is running or not? Since it seems to happen evening through morning, maybe we can cool the house down early evening and shut the AC power off overnight to see what happens, though that could take weeks to show it stops the sound. Is that what you mean? Completely cut power to the AC? Or just switch AC to "off" on the thermostat?

The humidifier should definitely not be running. Could a humidifier in the basement shake the floor of the 2nd story bathroom? We did test the humidifier a while back by turning the furnace on and making it humidify, and it functioned properly and quietly. We considered unhooking the electric wires to it to rule the humidifier out completely but didn't end up doing that step, so that'll have to go on the to-test list.

Thanks for your input

[ma0641]

Certainly sounds electrical-a pump, compressor, maybe an ejector or sump pump?

[hkstroud]

Is the water heater drain valve the best place to test the water pressure post-pressure-reducing-valve? Would a basement faucet work just as well

Pressure gauge will only fit on hose bib thread. Will not fit on laundry tub faucet.

The water heater flue DOES touch the gas line piping,

Is this dangerous?

No, I don't think so, but expansion and contraction might make a noise.

I'd slip something, like a small piece of pipe insulation, in between.

Is there a condensate pump in the sump hole?

Nothing in the basement is going to shake floor of the 2nd story unless it vibration through some rigid pipe.

Sewer is gravity drain, not sewage ejector pump isn't it?

[whatsthissound]

Pressure gauge will only fit on hose bib thread. Will not fit on laundry tub faucet.

Sorry, faucet is probably the wrong word. I mean this, like where the washing machine hooks up:

Is there a condensate pump in the sump hole?

Typical submersible sump pump

Sewer is gravity drain, not sewage ejector pump isn't it?

Sewer is gravity drain, yes

[hkstroud]

Pressure gauge will fit washer hose bib.
Could sump pump be making a sound?

[whatsthissound]

Could sump pump be making a sound?

It doesn't seem like it, based on where it is, and how powerful the sound and vibration through the house is. The sump pump can be heard on the audio recording during quiet times (when AC isn't running), and it just does its thing quietly and turns off. We tried dumping water in the sump pit to make it pump repeatedly, and it just behaved normally. I could always try setting the recorder on top of the sump pit sometime to see if it captures a louder banging sound than when it sits on top of the water heater.

[afaroo]

I am a bit confuse you said the bang noise happened after you replaced the water heater and you had no problem before correct, if the bang sound happened after the water heater replaced, I had two case after new whirlpool water heaters installed would hear a hissing sound and explosion sound every time the water heater would start called whirlpool they sent a technician adjusted the gap between the thermocouple and the pilot and that fixed the problem, Thanks.

John

[whatsthissound]

I am a bit confuse you said the bang noise happened after you replaced the water heater and you had no problem before correct, if the bang sound happened after the water heater replaced, I had two case after new whirlpool water heaters installed would hear a hissing sound and explosion sound every time the water heater would start called whirlpool they sent a technician adjusted the gap between the thermocouple and the pilot and that fixed the problem, Thanks.
John

John, thanks for the tip. Yes, there was no banging sound until after the water heater was replaced, expansion tank added, and AC serviced. It might require a technician checking it out eventually, after doing the water and air pressure tests mentioned earlier. The plumber has sent an earlier recording of the banging sound (before the hiss was discovered) to a water heater technician and the tech didn't recognize the sound. Maybe they'd be able to find something in person.

We've tried linking the banging sound to the water heater heating, and haven't been able to. Whenever the sound happened, someone would run down and touch the flue to see if it was hot and look at the pilot light to see if it's the only thing lit or if the whole burner is lit. There hasn't been a pattern we can find.