99 Winy With a Taping Noise From Heating Cooling System

My Winny started a moderately loud tapping noise inside the vehicle that sounds as if it was coming from write behind the radio or a bit to the passenger side. It’s not the engine or trany and sounds like something in the heating and cooling system. The tap is very rhythmic. Thoughts?

Search for "blend door operator"

Blend door actuator is the FIRST thing that comes to mind.
This is a door that moves back and forth to control how much HOT air is to be blended with the air entering the passenger compartment.
The heater core is always hot (at least when the motor is warm).
The interior temperature is controled by the position of the blend door.

When you adjust the temperature, a electric motor drives a gear that moves the blend door.
The clicking is likely the gear teeth clicking over each other.

This is a VERY common failure, which is why a search on "blend door" will get you a LOT of posts.
I was very lucky.....and never had a problem with this.

The blend door, which is driven by a electric motor is NOT to be confused with the diverter doors, which are driven by vaccum solenoids.
The diverter doors control where the air goes, such as the defrost, floor or vent.