Loud popping noise from ductwork when the blower turns off
The loud popping or snapping noise happens when the sides of the ductwork or return drop flex and collapse as pressure changes when the blower fan turns on and off. This typically occurs because the sheet metal lacks enough structural rigidity to hold its shape against the airflow pressure changes.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Checking if the filter is slamming when not being pulled
- 2Putting a piece of slip across the duct where it pops to stop the noise
- 3Adding an L-shaped length of metal spanning from side to side and screwed to the popping duct
- 4Checking the filter to ensure it is not overdue or too high grade
In their words
Unedited, most upvoted first, each linked to the thread it came from.
“Need to add structure to the return drop, thats most likely where you get the boom from”source ↗
“Everytime my blower fan shuts off there is a loud popping/snapping sound from the ductwork”source ↗
“Doesn't matter if it's heat or central AC.”source ↗
“The ribs still are not stiff enough to stop the sides from collapsing when the furnace turns on and off. Is there a way I can fix this”source ↗
Where this came up
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