Whistling behind Dash

[Cucv]

Would faulty or going out blend doors cause a whistling sound from behind the dash when the air is on? when I have the AC on it makes noise but when I have just air on it does not.

 

[Cucv]

Anyone?

 

[Doubeleive]

could be a actuator door, I would try to adjust all the settings up/down/defrost hot/cold and try to narrow it down to which one it is.