I've a new house with several fantech in-line fans. There's a grille in each room, and that has a butterfly flapper inside. It's been pretty windy here lately and the flappers are tapping. Drives me nuts. Apparently the wind across them is causing a negative pressure situation and that draws the flappers up enough to just to make them tap.
There's several of them up there and they all seem to doing this. They're not all on the same pitch or segment of the roof.
I'm wondering what choices exist to eliminate this? I'd be tempted to just put some felt or something along the inside of the duct down in the room. But I'd be willing to have the roofers put something different up there if it eliminated the problem entirely.