Put an End to Exhaust Vent Chatter
When the wind blows just right, the flapper on an electric dryer or exhaust fan vent can open and close, causing a chattering noise. One solution is to put a little weight on the flapper, enough to resist the wind, but not too much or the flapper won't open when the dryer or fan runs.
Attach a few small magnets first and then run the dryer, hood vent or bath fan to make sure the flapper still opens. If the chatter is gone, great. If it persists, add another magnet. Always check that the flapper still opens when it's supposed to. Once you get the right balance, add a dab of adhesive to the magnets to keep them in place. You can get a 1/2-in. x 30-in. magnetic strip at home centers for a couple bucks.
For noisy plastic vents, try attaching small washers with a dab of clear silicone. Note: These flapper-quieting tips are not for use with gas appliances.