I have been holding off on asking this question to the masses as it is a weird one, but I have had the car for 7 years now and its time.......1968 Charger Non A/C.

Basically, I get a bee buzzing noise from my vent/ air box under dash area when that passenger side vent is closed. It starts at a MPH range around 35 and if I crack the vent it goes away. I suspect the air pressure is causing some type of strange internal vibration. The entire heating system functions properly and is in good shape so I thought I would throw this out there before I consider a tear down.

Any one experience this noise from the vent system in the past?