What is the loud irregular plasticky clicking sound coming from behind dashboard on passenger side of a 2002 Ford Fiesta?

The loud, irregular, plasticky clicking sound you hear coming from behind the dashboard on the passenger side of your 2002 Ford Fiesta is likely caused by the blend door actuator. The blend door actuator controls the flow of heated and cooled air into the passenger compartment by adjusting a blend door in the heating and ventilation system. If the blend door actuator fails, it can make a clicking or popping sound when trying to move the blend door. Other possible causes include a faulty blower motor, a stuck or broken blend door, or a problem with the HVAC control module. It's best to have the vehicle inspected by a qualified mechanic to accurately identify the source of the sound and determine the appropriate repair.