If your vehicle is showing clicking or tapping noise from behind the dashboard, here are the most likely causes and the parts you'll need to fix each one.
The small electric motors that control the temperature and airflow direction behind the dash use plastic gears. When these gears strip or break, the motor continuously slips, causing a repetitive clicking or tapping noise when you turn on the car or adjust the climate controls.
Leaves, twigs, or other debris can bypass the cabin air filter and fall into the blower motor's 'squirrel cage' fan. As the fan spins, the debris hits the plastic housing, creating a tapping noise that speeds up or slows down with the fan speed.
Relays are electrical switches that make a faint click when activated. A failing relay, a short circuit, or a bad ground can cause a relay (like the turn signal or accessory relay) to click rapidly and loudly behind the dashboard.
If the clicking happens primarily when you turn the key or press the start button, a weak battery or loose battery terminal can cause the interior relays and the starter solenoid to click rapidly due to insufficient voltage.
Aftermarket security systems or remote starters use external relays that are often zip-tied under the dash. If poorly installed or suffering from a loose ground wire, these relays will click erratically while driving or parked.