heater goes tick-tick-tick!

I have a 91 c/k1500. The housing behind the heater blower starts ticking very rapidly for about 30 seconds before and after I turn the ignition on or off. There is also no heat coming out of the vents. I tore down the passenger side dash down to the heater core and cannot figure out EXACTLY where the ticking is coming from. Any advice would be greatly appreciated.

you dropped something down the vents that is hitting on the blower motor blades and is also blocking the vent door. pull your heater motor and see if you can reach in and pull out the problem.

I think I had the same problem with my 93 Z-71, it sounds like the same problem. It hasn't done it (recently) but it sounds like the solenoid that controls the damper door. It is located under the dash on the pass side, is that where your noise is coming from? And does the tick timing stay the same, or does it slow down until it comes to a complete stop? If it maintains the same speed until it stops, thats where you should look, I will look at mine when time prevails.