Pontiac vibe clicking

I have a 2003 Vibe. Recently something inside the dashboard on the passenger side has started making a clicking sound. It’s regular like a metronome, about one click per second. It only stops when I hit the button to use air from inside the passenger cabin. I’ve opened the hood, and the sound is not audible from inside the engine compartment. Help!

Also have a 2003 vibe with clicking sound from the passenger side of dash. The speed of clicks increases with fan setting - is slow on lowest fan setting, faster on highest fan setting. However, mine is audible when I lift up the hood with the car running. Also, the blower motor sounds like it pulses. Does yours do that?