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.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Checking if the filter is slamming when not being pulledDid this help you?
- 2Putting a piece of slip across the duct where it pops to stop the noiseDid this help you?
- 3Adding an L-shaped length of metal spanning from side to side and screwed to the popping ductDid this help you?
- 4Checking the filter to ensure it is not overdue or too high gradeDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, 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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