When the vent hood fan turns on the air pressure rushing out forces the vent to open breaking the magnetic force holding the flapper closed.
Roof vent flaps in wind.
Cheap metal vents can be very loud and obnoxious in the wind.
These types of vents are easy to remove and clean which prevents clogging.
This actually seemed to work pretty well.
If the noise drives you crazy new spring loaded backdraft dampers 9 to 30 depending on the size should solve the problem.
There are a couple of things that can help to reduce the problem.
Often a stiff wind will open vent dampers causing them to periodically clang shut.
The high quality plastic and resins used are durable uv resistant and will last for years.
Vertical vents were a source of whistles and banging flappers.
A noisy vent cover.
This pressurises the house a bit on one side and depressurises it on the side of the exhaust hood.
With gusts of wind that causes air to actually move from the house out through this exhaust duct.
Keep in mind that wind blowing across a vent opening creates a vacuum the faster things blow thus creating flap rattles as the wind gusts.
This is one that has been bothering me and a lot of my neighbors.
When the vent hood fan is shutoff and the airflow diminishes and the flapper begins to close.
We had a satisfied customer submit this video to us to prove a point.
This video is my attempt at keeping mine from clanging in the wind.
Disconnect the vent tube from the problem vent in the attic.
The vent in the video is.
How to keep a roof vent from flapping.
Climb onto the roof and locate the vent that is causing the noise.
This is usually just a few screws.
Lift up the edges of the surrounding roof.
Sometimes altering the cap on the vent reduces the vacuum.
Set the screw aside for reuse later.
Oversize flanges accommodate water tight installation.