If your vehicle is showing rapid clicking noise from behind the dash when adjusting climate controls, here are the most likely causes and the parts you'll need to fix each one.
The small plastic gears inside the actuator that controls air temperature, vent direction, or recirculation have stripped. The motor keeps trying to turn, causing the broken gears to slip and click rapidly against each other.
Leaves, twigs, or debris have bypassed a missing or torn cabin air filter and are hitting the spinning blower motor fan cage. The clicking usually changes speed when you adjust the fan dial.
A failing electrical relay is rapidly opening and closing due to internal wear, a bad ground, or poor voltage. This creates a sharp, metallic clicking sound from the fuse/relay box area under the dash.
The main climate control panel is malfunctioning and sending erratic electrical signals to the dash actuators or relays, causing them to twitch and click continuously.