So we bought a house built in 1986 last year. Over the past year, I've been able to identify a single (and I do meant SINGLE) knocking sound which generally repeats every 20-60 seconds until I go to search for it.

I'm pretty sure it has something to do with the structure, and presume my body weight & position, but thats where it gets strange. I hear it when I wake up in the morning. It does happen sometimes when I lay down for bed, or sometimes in the middle of the night. But as you might be gravitating to, I hear it when I am in bed. If I stand up, I still hear it. As soon as I start walking to go find it, it stops.

Now is it a critter? No. We have cats, but no matter, my wife or daughter can go look for it rustling through the house and basement, and outside and it continues for them, but all they have ever identified is that they think it comes from the heat vents in the basement under our room. It doesn't. Heat, AC, nothing, moving pipes, turning the system off, it happens when it wants to in all of the above. I have also moved and or secured the pipes/vents to no avail.

It's not something I can really call a contractor in for as it doesn't always happen when I go sit on the bed. It happens at all seasons and weather conditions.

Now, given that I can be in bed to instigate this sound, I've tried moving (and not moving) to promote its occurances or cause it to cease but it does not. Therefore, I can lay in bed for hours, and not move a muscle, and listen to it for hours, every 10s, 20s, 120s, etc. a single "pop" or "knock"

I am trying to capture the sound on a recording so I can share it. But consider this: take a #2 pencil and wrap it against a 2x4... but do it lightly, e.g., drop a #2 pencil on a piece of paper on a carpeted floor - that is a great replication of the sound.

I'd like ideas of what it can be, and how to catch/isolate it, so I can finally wake up to a silent morning. :)

I really do believe it's structural (which is why I mentioned the year built) and think its a support beam moving on a nail or plywood, but as aforementioned, it happens with me completely still, and I cant instigate it, so why would it be the same repetitious sound endlessly....

Here is some photos of the suspect area: Basement under bedroom, where clicking is heard

UPDATE (11/7/2018): At the link above I just uploaded a video file with the noise. There is 1 (maybe two) heater unit click noises, you can distinctly tell them apart from the ones that sound wooden. (listen for the sound of a drop of water, or pencil tapping). Also, and this is potentially attributable to the "intermittency" of it all, is today is a windy day, and no one is in my bedroom. I just cannot isolate the noise well enough to locate it.

This question had a bounty worth +500 reputation from noybman that ended 7 hours ago. Grace period ends in 16 hours

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Offering the max I can offer because I really really want to solve this.

  • When I lived in a wood house there was a constant ticking, knocking, as the house expanded or contacted due to thermal changes. Maybe? – James from NZ Nov 4 at 21:01
  • I'm of the same train of thought, but it doesn't change temperature drastically in a the same moment I stand up :) Oh...amplifying info maybe: it is a ranch, plank&batten, full basement. While it sounds like its "outside" we unanimously agree it is floor (or basement rafters) area focused. vs. actually outside or roof. – noybman Nov 4 at 21:20
  • The description corresponds to a typical HVAC expansion tick. Can you correlate it to either furnace activity or plumbing drains? – isherwood Nov 7 at 2:49
  • @isherwood, have a listen to the video file linked above. I'm very confident it is not furnace. I'll have to listen to the sewer pipes to see if they are relatable – noybman Nov 8 at 9:36
  • My first instinct was some kind of glue failing a little bit at a time all over the place. Is there some kind of bonded layer in your floor system? Joist to plywood? Tile to plywood? If the problem is at a single position, then you can narrow down that position if loading distorts the sound. How about systematically moving a car jack throughout your floor system to apply some horizontal thrust between floor joists until the sound changes pitch, frequency, etc.? – popham Nov 9 at 7:46

Hmmm...let’s see: 1) immune to cats stalking, 2) triggered by you stalking it, but not your family, 3) occurs on regular basis (not affected by seasons), 4) occurs at regular intervals, but somewhat random, 5) single tick, never multiple.

Sounds “mechanical”, except for item #2. Could be air sampler for HVAC for heating controls or air sampler for environmental purpose, like radon test.

Battery backup? Electronic control or monitoring (house alarm)? Are there any devices hanging on a wall that you do not know what it is?

  • No there aren't any electronic devices in the area. The AC unit is on a different outer wall. The noise occurs when power to furnace & AC is off. Most common in the morning. Yes there is air ductwork near this, but I have messed with it enough I'm pretty sure it isnt the culprit (no change in sound, and it is not metallic) – noybman Nov 7 at 4:21
  • I added some pictures of the expected suspect area – noybman Nov 7 at 4:32
  • @noybman Structural issues do not occur on a regular basis nor regular intervals. It’s possible that a structural tick could be triggered by a larger person only, but friends and neighbors could trigger it too. Based on the size of the joists, checking could occur but I’ve never heard of noise generated from lumber shrinkage (drying out). – Lee Sam Nov 7 at 5:43
  • I'm ~300, counts as larger. But my wife and daughter together get near that. I could have a friend come over, might be a good way to be able to investigate once it gets going. If structural doesn't make sense, I'm boggled. Anyone have any ideas on how I can capture it by some remote recording device? – noybman Nov 7 at 23:17
  • For the ticking to be a structural issue, it seems like it would be from movement. Either movement from thermal change or movement from moisture change – Lee Sam Nov 8 at 1:19

You say it's not your ducts, but I just listened to your video and I've heard that sound before, it's the sound of expanding metal uptight against wood and slipping. The fact that there's a similar noise coming directly from the vents at times just means that it's coming from hangers that are having trouble holding onto your duct work, some of which has padding between in and the ducts preventing the resonating tinny sound, where as in other places it's not dampened and thus you hear it along the duct.

It's clearly not a critter so it's better off just left alone.

Loosing some hangers may actually be the solution.

Similarly, changing how fast your hvac system heats up / cools can help you troubleshoot. Open all the registers in your house and take note of how often you hear your noise. Now on a day with similar temperature and humidity try the same test with only one register open. If lower airflow means less noise then reducing your your blower fan speed should help and vice versa.

Other fixes to try if it's still bothering you:

If the sound is relatively new (you've lived in the house before and this is the first season where it's been a problem) you can try to tighten down or loosen all screws and hangers related to the duct.

If the sound has been there for almost as long as you've had the house, you can try adding rubber or plastic spacers to your hangers and anywhere else the duct-work might be in contact with the wood.

However, my guess is that your particular noise is buried inside an inaccessible part of your house, else you probably would of pinpointed the cause of the problem. Thus the next most reliable solution aside from ripping out and replacing all the duct work with properly insulated circular ducting, or a different kind of HVAC system is to add an acoustic duct liner.

If it were my house

If I was experiencing the same sounds those ducts also carry AC, i'd just wrap the exposed duct-work with neoprene insulation to prevent sweating and reverberation of the sounds and the next time I change the flooring add an acoustic padding.

Similarly, I might try reducing with the blower fan speed depending on how accessible that is.

If you are rich and can afford to pay for quiet:

If I were rich, I'd just remove the entire central air system and replace it with a ductless mini-split heat pump system. Not only will this eliminate the noise, but you'll have:

  • Better zone control.
  • A large space in your basement freed up where your furnace and control system currently is.
  • No unsightly ducts running though your basement and taking up space in your walls if you ever choose to finish off your basement.
  • I've tested it with the breaker off to the unit, but tonight I used an automobile stethescope and listened to numerous sections of the ductwork, the sound did not come from the ducts. – noybman Nov 9 at 3:27
  • Like I said, metal expanding on wood and slipping against wood. Since it doesn't resonate down the ducts, I'd assume there's some sort of padding between the ducts and hangers. Very quick temperature swings are your most likely culprit. Does this ever happen when the furnace isn't running? – virtualxtc Nov 9 at 4:52
  • Yep, all of the time. Thats why I described it in the OP. No pwer to the unit at all from the breaker box but it still happens. I dont have any breezy or noticibly drafty areas in the house so if I had a blower door test done I'd expect it to be decent grade. – noybman Nov 9 at 5:01
  • Well, the only other time I've heard that kind of woody pop was when floor spans were failing / shifting due to some foundation issues. But yours definitely sounds more like a slipping than a cracking. – virtualxtc Nov 9 at 5:05

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