Can you localize the source of the noise? What area of the dash (I assume its coming from the dash) is it from? If you have a faulty actuator or broken mode or blend door that will help isolate the cause. If its an actuator or door problem, its MOST likely to be with the cold air bypass door or actuator (located near the left hand floor duct) or with the defrost door or actuator (can be accessed by removing the instrument cluster). If you can get to where you can access these actuators you can check to see if they are moving or not while you change settings. Of course remember, even if the actuator moves the door could still be stationary due to it being broken ( they are only plastic after all ).