Clicking sound on my Suburban

I have a 1994 Chevrolet Suburban. It has a new clicking sound when I turn on the ignition that lasts about 1 minute. It is a very evenly spaced sound coming from somewhere under the right side of the dash - probably in the air system. The sound stops after about 1 minute and does not come back until I shut off the engine. At that point it comes back for about another 1 minute. It does not seem to cause any performance problem in either the AC or the engine.

My questionn is, what is it and how do I correct it?

I also have a 94 Suburban with the same sound. Mine does it when I turn off the car, It sounds like I left the turn signal on. I hope you get an answer so I could fix mine.

The answer was a small gear which controls the outside/inside air vane located behind the glove box. That gear had lost one tooth.