Snap, crackle & pop

Had a call from a friend regarding his parents house. It is a 1987 build, 1850 sf, slab on grade and truss built. They bought the house in 2020. House has had recent updates before the purchase. New paint, new floors, some new fiberboard siding on gables. This issue, most pronounced in the winter, is loud snapping sounds. It generally occurs when the heater is running. Heater is 105,000 btu natural draft gas furnace. The sounds usually come from the south side of the house. Went over there this morning and I did hear a small expansion type pop coming from the south wall after the heater had been on for about 8 minutes but the owner said that was very mild. Sometimes it sounds like a gunshot. There was no signs of movement on the walls or ceilings, but the ceiling had had the popcorn removed and new texture was done throughout. When I got up in the attic I noticed the house originally had cedar shake shingles that were removed and OSB decking installed with newer asphalt shingles and ridge vent. All trusses were in original condition, no modifications or damage. I did notice that as I walked across the trusses and leaned against the webs there was a lot of creaking, more than I have noticed in other attics. There was no indication of structural movement on the exterior.
I know this isn’t a lot to go on, but any ideas what may be causing the loud popping sounds?

I’d put my money on the ductwork.


When the temperature in the materials used to build the house goes up and down, the materials expand and contract with the heat and cold. This causes popping sounds in the wood and/or other materials. It is usually heard when warming up in the day and cooling down at night.


I agree with Ryan and JR. :smile:


I failed to mention, the ducts are metal in slab. Would they react as the link explained?

I would sure think they could. I have very little experience with ducting in slabs though. Not a popular option in my area.

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If the return duct is undersized or the gage is too light, it will “pop”, when the blower starts up.

Take the door off the furnace blower compartment and tape the door switch. Start up the furnace and see if the pop goes away. It will let you know if that is the problem and needs to be fixed or time to move on to the supply.


Wood flooring, Vinyl interior trim? or laminate flooring?

What Jeff said. My old house in Tennessee had this problem years ago. It had a packaged unit outdoor Trane electric heat pump and the return was slightly undersized. Sometimes when the blower started up it would make a loud pop as the metal ductwork would get sucked in slightly, bow the metal ductwork inward and then once the pressure stabilized it would pop again when it bent back into place. Since the return area was difficult to modify where it was within the house structure, the HVAC contractor solved it by fastening a few shim blocks where it was prone to bending and then fastening them into place to keep the duct from moving again at those locations.


Bedrooms are carpet, baths are ceramic tile and the rest is LVP.

The popping sound I heard appeared to come from the wall, about head high a foot or two in from the corner of the room.


The squirrels are having a shoot out for home turf in the walls. :stuck_out_tongue_winking_eye:




My last house had a duct that fed an upper level right next to the family room where I usually hung out in the evening. Every time the heat kicked on and the duct heated up I’d get a crazy amount of snaps and pops right through the wall from where I sat. I could go into the crawl space and pull the duct off the back of the wall and the noise would subside for a bit but it always seemed to return a few weeks later and I’d find the duct back against the sheetrock. I was too lazy to ever fabricate some method of holding it off the wall permanently but was amazed at how much noise an expanding metal duct could cause.

yeah you are right Rayan