Could it be the refrigerator compressor kicking on? Or off?

Hello, Chibimimi, and thank you for your post. No, that's a soft little hum. The refrigerator was also purchased after the noise first began.

The noise in question is quite a bit louder. As I stand in my kitchen near the bay windows looking out into the yard it sounds as though it's coming from just below me in the basement. So it sounds like it is near the outside wall vs further into the basement where the sump pumps are located. But when I go to the same spot in the basement, I don't hear it as loudly. It's almost muffled sounding. That's why I thought I might hear it standing on the patio just outside the bay window, but I hear nothing out there.

I hope I'm explaining that well. It's all a bit puzzling.

How old are your toilets? Sometimes a toilet tank seal will fail slowly and let water flow at random moments, which could account for the water pipes vibrating elsewhere in the house.

Hi Circuspeanut. Thank you for asking. The toilets are more than twenty years old, although the seal on at least one of them has been replaced during that time. Is there any way to determine whether or not it could be the seal without calling in an expert at this point?

Forgive my ignorance, but aren't there pipes that lead to a septic system outside? Could there be something wrong with that?

I wish the noise happened regularly, because then it would be easy. I would call the plumber and he would hear the noise and start his investigative process. I have discussed it with him by phone and all he can say is that he has no clue without having heard the noise. This has been very frustrating, as you can imagine.

Pipes and moving water can make some odd noises, sometimes away from the source of the problem. Toilets can leak in two places - between the tank and the bowl or the fill valve itself. The classic test for a leak between the tank and bowl is to put food coloring in the tank and wait to see if any of the color appears in the bowl. The other option is to shut off the water supply, note the level of water in the bowl, wait an hour or two, and check the water level again. The fill valve is something you would have to observe. You would hear the tank filling from time to time when the toilet hasn't been used. I'd be incline to think that those would be occurring more frequently than what you are describing and any odd sounds those events caused in the pipes would be something you heard when you used the toilet.

Has anyone else been around when you heard this noise? I'm not questioning you but rather suggesting that two sets of ears might be able to triangulate on the source of the noise more easily that one set.

Forgive my ignorance, but aren't there pipes that lead to a septic system outside? Could there be something wrong with that

A ha! If you have your own septic field, I take it you are not on city water services and have your own well, also? My parents have their own well and it requires an electric well pump to bring the water inside the house.

Definitely check that out if you haven't already! It would account for the frequency you mention (both the sound and how often you hear it). It is not unlike a sump pump in sound, but deeper and harder to locate with your ears because it is located right outside the house wall in the ground. And this would definitely account for the water pipe noises.

Just another possibility; someone well-versed in plumbing like the above poster will have more insight for you.

Hello, Mike, and thank you for weighing in. I will try the food coloring test and see what happens.

I can tell you that I do have a problem with two of the toilets sounding as though they are 'resetting' suddenly when nobody has used them for hours. I do not think that is the correct term for it so hopefully you know what I mean. It sounds as though they are filling up again after being flushed. And now that I have typed that out I feel truly ignorant because I thought that might have something to do with needing to adjust the float valve. Is that what it's called? And I don't know how to do that and have spent more money than I care to on home repairs, so wanted to avoid calling a plumber for an adjustment that I thought didn't matter.

Yes, others have heard the noise and asked, "WHAT the HE!! is THAT?!" It really is disturbingly loud.

Circuspeanut, now you will see how ignorant I am about these things. I am on city water and do not have a well. I guess that rules that out anyway.

Just because you can't hear it outside the house does not mean the sound is not coming from outside. Sometimes certain frequencies will resonate with materials in various parts of a house from a long ways away. I went through the same thing with our house. I kept hearing a periodic faint noise upstairs in our house that could not be heard outside or downstairs. It turned out to be from a small dairy facility over 10 blocks away. It was a big pump that when turned on amplified the sound by vibrating the glass of a bedroom window. Once I knew what was causing the sound (not irritating in any way), I paid no attention to it. The windows have now been replaced and the sound is completely gone. I only discovered it one day when I was walking by the facility when the pump turned on and I thought "that's the sound!"

Someone else had a problem like this. The thread is titled "House is humming, literally" and has been bumped up. HTH

rmtdoug, thank you for your post. How interesting! I never even considered such a thing but I can see how that might happen. If I rule out all else, I may have to just resign myself to it being something external like that.

Northbound, how kind of you to bump the thread. I will go look for it now. Thank you very much!

When sump pump empties into drain field you can hear it.

My well pump makes a huge racket when it kicks on. When the icemaker in the fridge refills with water, you can hear the water run for a few seconds, then stop. I have central AC on the furnace that has a condensate pump which comes on whenever the water level lifts the float enough, and pumps the water through a small hose to the outside of the house. I also have a dehumidifier in the basement that is piped to the AC condensate pump so it empties itself.
Toilets that are leaking water, either past the "flapper" in the bottom of the tank will refill when the level drops low enough to lower the float and activate the fill valve. Water hammer noise is common on toilet fill valves, so this could be what you're hearing. Replacing the flapper is easy and inexpensive, just turn off the water to the toilet tank (there should be a shutoff underneath) and flush to drain the tank. The flapper is often a rubber thingy that is stuck onto little hooks on the sides of the overflow pipe. Just unhook it and take it to the hardware store for a replacement. Other types might be a ball shaped thing stuck onto the bottom of a stiff vertical wire. It probably unscrews.
If you determine with the food coloring that the water in the tank is leaking into the bowl, and you encounter something different in your tank setup, a description of what you see in there would help.
Jo