Could be the actuator or blend door motor.
Remove glove box and locate the clicking.
Make sure it is not a relay.
The blend door actuator is on right top of ac/heater housing.
With glove box out you should be able to see and or feel it.
Is the clicking coming from it?
Check the how to section. For pictures and how to on it.
Lot of good info there.
http://www.automotiveforums.com/vbul...d.php?t=574779