Oil canning (noisy ducts) in walls

Hello everyone.
The ducts in my house make a loud booming noise when the heat turns on and again after it cools down. Sounds like someone is banging a metal trash can with a hammer. It's so loud that I'm ashamed to have friends over.
My house is on a crawl space, and I have no easy way to reach the ducts. Can I do anything to fix this? I just got a new heater and decided not to get a humidifier (since the old one didn't do much good). Will a humidifier help the problem?
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You need to find the section of duct that is flexing and causing the noise. It's not unusal for that section to be close to the furnace. Someone needs to look, while another person cycles the blower.
A variable speed blower that slowly ramps up in speed might solve it too, if a new furnace is in the cards.
 I just got a new heater and

No. Why would you think a humidifier would have anything to do with it? Humidifiers work. Are you sure the old one was even working, installed correctly, etc?
I guess a new furnace isn't in the cards then. What did the installers say when you pointed out the duct noise to them?
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If you manually turn the blower on and off, without the furnace heating up, is the noise there? You need to tell if it is an expansion problem due to heating the metal, or if it is the duct flexing under the air pressure. You should be able to hear which wall it is coming from, and then locate it better using a listening tool, a rod held to the wall and the other end to your ear.
Once you are suspicious as to the location, cycle it several times to be more sure. Then insert a stiff wire or knitting needle thru the wall till it touches the duct. Listen again while the noise reoccurs. If you are close, you should be able to feel a vibration in the wire/needle. If you do, then you know where the problem is. From the attic, maybe you can slide a piece of wood down into the opening, along the side of the duct, to push against the duct and stop the noise.
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On Feb 20, 1:42 pm, " snipped-for-privacy@sbcglobal.net"

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Thanks for the responses.
Trader4: The furnace is just a few months old -- its a two-stage, variable speed heater, and according to the reviews it's a good heater. The humidifier? I just mentioned it because I had a humidifier with the old heater and I don't remember this kind of noise. So it was a stab in the dark.
hrhofmann: I'll take your advice and report back to this thread. Concerning the attic, the noise is definately on the first floor, and the attic is not a walk-in attic. If I locate the noise, can I cut through the dry-wall and fix it there?
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Dom wrote:

Since the furnace is only a few months old, could you call the installer and ask them to come back and check out the problem? Most installers give a 1-year guarantee of their own regarding the installation in addition to any longer-term guarantee that comes with the unit itself from the manufacturer.

Maybe ..., or least that's my guess. But I would try to have to installer of the heater come back first before doing anything on my own.
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I'd call the furnace installer, and ask his help. Might be possible turn down the fan. A humid- ifier might circulate some of the air back into the return, so it may reduce the pressure coming from the furnace.
Christopher A. Young Learn more about Jesus www.lds.org .
Hello everyone.
The ducts in my house make a loud booming noise when the heat turns on and again after it cools down. Sounds like someone is banging a metal trash can with a hammer. It's so loud that I'm ashamed to have friends over.
My house is on a crawl space, and I have no easy way to reach the ducts. Can I do anything to fix this? I just got a new heater and decided not to get a humidifier (since the old one didn't do much good). Will a humidifier help the problem?
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On Feb 20, 1:57 pm, "Stormin Mormon"

Good points, Stormin. I had called the installer about the noise from the air-flow, and he reduced the speed already. Said he can't reduce it anymore or I won't get maximum efficiency. I didn't ask about the duct noise, so he might have some advice there.
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Never know. It's honorable, to call the installer, and give him the chance to follow up. I know, I sure resent it when people call, and they have asked everyone except me, and done all kinds of self help except calling the installer.
Christopher A. Young Learn more about Jesus www.lds.org .
Good points, Stormin. I had called the installer about the noise from the air-flow, and he reduced the speed already. Said he can't reduce it anymore or I won't get maximum efficiency. I didn't ask about the duct noise, so he might have some advice there.
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.

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Air flow noise when heating or for AC? Seems kind of odd that a new variable speed blower would make noise that requires it to be run slower. I have a Rheem that isn't anything special and you can't hear any air real air noise when heating or cooling at 2000CFM. You can hear the blower motor a bit, but not the air.
 I didn't ask about the

I would definitely get them back. If the noise didn't exist before the new install and now you have a bang, then it would seem likely it's related to the install. I'd check the ducts closest to the furnace, because it would seem given the info that is where it's most likely to be. They had to screw with that portion of ducting to put the furnace in. They didn't have to screw with ducts in the walls.....
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wrote:

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The noisy air flow was from the heater; the AC is new too, but I haven't turned that on yet. Come to think of it, I don't know if the noise was from the heater motor or the air flow itself when he fixed it by turning down the speed. The heater (and AC) is a Rheem.
I take it the opinion here is to call the installer. That's what I'll do, then, before I go crazy with DIY stuff.
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If the air noise issue was from heating mode, I don't think you're going to be happy when it's in AC mode. The AC airflow rate is typically 50%+ higher. I have a Rheem and it's something like 1200 cfm for heating, 2000 cfm for cooling. I paid closer attention to noise after this discussion. I guess some of the noise is air flow noise, not just the blower. But whatever it is, it isn't objectionable and is a lot less noticeable than the 25 year old unit it replaced. Part of that is because with a variable blower, it ramps up slowly and turns off slowly.
 Come to think of it, I don't know if the

As I said, if it was me and the furnace is accessible, I'd take a look at the ducts near the furnace while someone cycles the blower. I like to know as much as I can before any service guy shows up. That way if they are blowing smoke, I know it.
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wrote:

I had an inaccessible duct doing something similar. To stop it I got a length of PVC pipe and forced it into a bowed shaped so that the two ends were against one side of the duct and the bowed out part was against the other side. That put pressure on the duct to make it stop moving with changes in air pressure. I made it "bow" by jamming it in at one end, bowing it, and then fastening down the end I could still reach.
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Hmmmm. Interesting. By "bow" do you mean "U" shape? And since your duct, like mine, is inaccessible, did you just go through a vent? What if the noise is far from the vent?
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wrote:

Not nearly as bent as would take to form a U. I used about a 8 foot length of pipe in a 1.5" wide duct so it was a lot more like the bow in the "body" of a bow and arrow. Yes, I went in thru a vent. If it's too far away... don't know. Mine was with in the roughly 12 feet that I could get to from the vent.
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