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We bought a new house a few months ago. I do not recall hearing this noise in the summer, when the AC was running, but then I wasn't in this room that much so I am not sure if it was happening.

We have a 3 floor house. HVAC system is in the basement. In the top floor, there are two air ducts right next to each other, both columned by dry-wall. One goes up to the attic and I assume feeds the air to the other rooms. The other is the return. The other end for both is in the basement.

The space for the duct is next to my office room.

When the heater is running, every now and then I hear a tapping noise coming from the duct. If the heater is off then no noise. Again, not sure if the noise would be there with the AC on.

It sounds like if a wire was tapping against something but there are no wires inside the ducts -- not that I know of.

I cut a 4" square into the drywall in front of the return duct and the sound is definitely coming from near/in/around the return duct.

There is no insulation around the return duct -- so its just hollow space.

I don't mind doing some work to identify the root cause but I have no clue where to look/start.

One person claimed it has to do with the lack of insulation because the air duct gets hot and is tapping against the wood beams. Could it be that? Any cheap fix?

I am including some pictures too.

from top floor,pointing to where air ducts are

opposite side of the first picture, from inside the office, looking at where the air ducts are

behind wall #1

behind wall #2

behind wall #3

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  • Mine is more of a tapping then pings resulting from the ducts popping. – IMTheNachoMan Dec 4 '20 at 21:22
  • In my experience the phenomenon manifests more often as tapping than pinging. It all depends on the local structure of the ducts and whether they're slipping against lumber or oil-canning. – isherwood Dec 4 '20 at 21:29
  • You know when you go into a pet store and you walk up to the aquarium or enclosure and tap on the glass to get the attention of the creatures inside? You are the creature inside ! – Alaska Man Dec 4 '20 at 22:20
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    To see if it is caused by temperature (expansion/contraction) or by airflow (maybe some loose tape or a flap of something caught in the duct and blowing around), you can try running the system on Fan-Only for a while and see if you get the same noises that you get when heating. That won't solve the problem, but it'll narrow it down a bit. (And yes, Fan-Only airflow could cause a bit of expansion and contraction, but not nearly as much as Heat or Cool.) – Doug Deden Dec 4 '20 at 22:48
  • As @DougDeden said, you can also turn on the AC for a short bit to see if cooling does indeed trigger it. How about if you intentionally close all the dampers for a while in the areas fed by this duct? (I have a tapping issue here on StackExchange I want to solve driving me bonkers so I feel your pain! Mine happens during winter more than any other season, but isn't triggered by the heat or ducts). Perhaps adjusting the airflow will help locate the source. – noybman Dec 4 '20 at 22:59
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I don’t insulate interior ductwork either. But I think what you are hearing is the expansion and contraction of the metal ductwork. The noise can go on for quite a while when heating and then again when cooling down.

Stopping this on a verticals run is really tough and no cheap fixes I have heard of consistently work. I have had people tell me they drilled a series of holes and shot spray foam and it helped, this same “fix” had caused the duct work to start buckling or oil can popping every time the fan turns on or off and this can get really loud. When that trunk line is more than 1 floor I will use a double layer of neoprene rubber 1/16” at the straps. This keeps the duct from moving on the framework the rubber spaces the duct and absorbs most of the noise but not all there can still be creaking at the joints I have tried to use silicone when assembling and jell type sealer that was available in the 80’s nothing has worked as well as the double rubber. The problem with double rubber is it takes space and is kind of expensive last would be almost impossible to do after install.

If you try spray foam make sure to not fill the entire cavity because when it expands this causes the oil can affect if you don’t like the tapping you will hate the oil can.

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  • Spray foam behind the drywall? – IMTheNachoMan Dec 4 '20 at 22:10
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    Yes, several people have told me it worked but one person I think he used two much. They called me to fix it after looking at I told them the best thing would be to remove the Sheetrock and see if that could eliminate the oil can effect but to eliminate the ticking was usually a major job and I could not guarantee totally eliminate the noise, he pulled the Sheetrock removed the foam then wedged some type of tarp between the metal and the wood. The friend that recommended me said the tarp worked fairly well and it was livable after they put the Sheetrock back on. For others the foam has worked. – Ed Beal Dec 5 '20 at 1:07

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