Blower direction loud popping noise?

[Olixir]

Hello, new to the forum! Just bought myself a 2000 Grand Prix GT with 93k miles.

One of the things that has been bothering me is that when I change the direction of the air blower (like from front to defrost, or defrost to feet, or anything) there is a loud popping noise that occurs, that scares the crap out of me!
Everything works fine, the blower works on all speeds (maybe a bit weak on high setting, but i'm not sure) and all directions.

Any idea on what this is? I swear i'm going to get in a wreck one day from this, it's really surprising how loud this popping/knocking sound is!

Thanks in advance!

 

[Scottydoggs]

sounds like one of the arms off the vac pumps is binding, or is broken.

this post will get you to where you can see the pumps working when you change the air flow. the car needs to be running or they wont change direction http://www.grandprixforums.net/showthread.php?t=21941&highlight=change+blend+door+actuators

its the round part with the arm off the top of it in the first pic.