Noisy interior a/c heater controls

[Andrew7]

My 93 C3500 454 Dually has weird noises coming from under the dashboard. They seem to get louder when accelerating. I have disconnected one flap actuator for noise already due to a clicking noise when you turn it off.

 

[GM01]

Assuming you're referring to the blend door motor, that clicking noise would be the motor grinding/skipping gears, broken teeth and all. I suggest replacing all the motors (3 total to the best of my knowledge) and go from there.

Here's a diagram, there are other threads around the site that are real helpful for stuff like that.