"The Hum"

No, I don't hear this here at my home, but .. can I ask if you have a low to moderate breeze outside?
My son was hanging doors in a new speck home (small three bedroom single bath and went in early one morning (4am) and heard a num low ringing sound , they covered the 4 inch vent pipe on the roof and found out it was ringing and it gets vibration from a slow 5 to 7 mile an hour wind .