email: cavebear2118 AT verizon DOT com

Friday, November 28, 2014

A Ghost In The Machine

Well, not a ghost of course, but there is a weird harmonic in my heating ducts that is making a disturbing noise...

There's a pattern to it.  The heating comes on about 22 minutes each hour when it is below freezing outside.  A function of the insulation of the house.  About 10 minutes into the heating cycle, this odd sound starts and stops.  Imagine a 1-note C on a wind instrument...

Not that I can tell notes, so imagine any moderate note on a wind...

Its obviously a harmonic in the ducts.  I can feel the vibrations if I stand on a ladder long enough and touch the ducts, but I can't pin down the source.  This isn't the first time either.  Previous years I've wrapped bungee cords around some pipes and ducts and it has stopped for the season. 

But it keeps coming back year after year.  I can't call it "spooky" because I haven't the least sense of superstition, ghosts, etc.  Its just a noise caused by a vibration I can't seem to stop. 

It seldom happens in daytime.  And I would notice it if it did.  You live in a house 28 years and you know every creak and squeak.  But at night (when it is coldest), it starts. 

Slowly, a tiny vibration at first.  Then a little louder.  And longer.  After a few minutes, it is going on for 15-20 seconds.  And a minute later it starts again.  Stronger and Stronger until it sounds like a trash truck driving by, but its not, and then the demon in the ducts stops suddenly.

I was up 3 times last night trying to figure out the cause.  It eludes me.  I can feel the vibrations anywhere I tough, but that stops it.  For a few minutes. 

I'm making light of this, but it really is driving me nuts and waking me up at night.  And I sleep poorly enough as it is.  It even got into my dreams...

Anyone had this problem, have any ideas on how to stop it?  I'm thinking of removing all the existing rubber straps that have "solved" the problem before.  Maybe if it gets worse, it will be easier to identify the real source...

And, BTW, I'm "pretty sure" I'm not insane...


4 comments:

Megan said...

Can the heating mechanics not sort it out? That is, perhaps this is one of the times where it will be better to call in the professionals and just get it fixed before you lose any more sleep. I can imagine how annoying it might be - it would drive me bananas.

Megan
Sydney, Australia

Megan said...

Dr Google may be able to help:

http://www.improvenet.com/a/duct-noises-after-furnace-goes-on

http://www.thisoldhouse.com/toh/asktoh/question/0,,1131823,00.html

http://www.horizonservicesinc.com/blog-posts/heating-services/what-causes-noisy-heating-and-air-conditioning-vents

Do any of these seem to touch on the likely cause of your noise?

Megan
Sydney, Australia

Ellen in Oregon said...

No, I don't think you are "insane" at least not about this noise in your duct system:) If it only happens at night when the temps drop, that sounds to me like an issue of contraction & expansion of the metal duct tubes. Maybe it only happens in the cold of night is because the metal contracts from the cold & then as the warm air is forced through the metal expands. The next most obvious cause, to me, would be a gap or gaps that only appear when when the metal contracts. I would think it might take a professional to actually view as much of the ducting and if they find no likely spots for gaps, could put some insulating foam at connecting parts of the duct. I was also thinking that after living in the house for so many years, I would think that the house has done a fair amount of settling and maybe points of support need to be shimmed up. I assume your furnace filter is clean because if a filter becomes clogged that can cause a vibrating whine because more force is needed to get air flowing through it. the metal in the ductwork starts to contract when the temp. drops to a specific point and the contraction is what allows the vibration to start. Did you check your furnace to see if it is still level on whatever foundation you have it sitting on? Also, check where the duct tube meets the furnace and make sure the connection is tight. I still think it has something to do with temp. changes making some gap temporarily allows air to vibrate or make that high pitched vibration. I think your problem is fairly common and is caused by everything from nearby highways sending vibrations into people ductwork to bee hives. Sorry, I have probably not been of any help. I really do think it is created by a small gap that only appears when the metal contracts & when the air warms up, the metal expands & stops the air from getting through. Hope you can find the cause before it drives you crazy.

Andrea and the Celestial Kitties said...

oh man, crazy noises like that drive me nutty! I kept hearing a weird noise every time the heat came on and it wound up being the paper we had put over the vent hole was flapping.. Cutting holes into it didn't help, and eventually it fluttered loose of the push pins. My cousin has the vent covers, painting them.. I think it's time to get them back!
Hope you find your mystery vibration and get rid of it quickly!