1994 Chevy Blazer noise under the passager side

I have a 1994 fullsize Blazer and when you turn on the truck there is a clicking noise under the passager side under the glove compartment it only does it when you turn the truck on and off. I look under the dash and it looks like there is a vent door that is not opening and or closing. could you point me in the right direction of a fix to my problem, and a estimated cost?It drives my Daughter Nuts