In CYV's the fan vents into the attic, maybe some have a roof vent. Either way there is no need to get in the attic or on the roof.Turn off the fan first. The trim ring & fan are easy to remove, just a couple of screws. The fan body must be gently pried out. Looking at the flapper you will see that it stays open normally. Maybe bad design or angle. When wind blows & pressure goes uo in the attic the flapper shuts, causing the noise. If you have a ceiling fan there is some lead tape in the kitchen drawer. As suggested, stick a 1/2 - 1" piece (cuts with scissors) on the lower edge of the flapper so it now closes normally. For insurance you can also stick a small piece of felt at the bottom of the housing where the flapper hit. Replace the fan & trim. Now the flapper will be closed normally- no noise with the wind, no cold air. The vent function will work as normal if you did not put too much weight on it. Over six months so far & no noise!
Steve
