Fan Noise, Nissan Altima

"windshield setting?" Is that the defroster setting? (sorry I've never owned a Nissan). All cars have what are called "mode doors," which direct just where the AC/Heated air is directed via the vents. The mode doors themselves are moved by "actuators," which are small plastic gear boxes and little electric motors. Chances are your actuator for one of your mode doors is broken and the clicking you hear is it trying to move the door but it's just grinding it's little plastic gears. A little troubleshooting will help you isolate which actuator is the problem. Google mode/blend doors for your make/model for diagrams of your dash's layout. Then be prepared for the task of actually swapping out the bad part, as getting to these actuators can be tricky.

Thanks.