Does anyone know what the small dime sized thing that looks like a vent above the inside of the drivers side door is?

 

I am assuming that you have a 2nd gen, likely a 98+ truck with automatic temperature control for the HVAC system. That is the inside temperature sensor used by the HVAC system. It has a small fan to circulate air over the sensing element that can sometimes get a bit noisy if it builds up with dirt/lint. If that happens you can blow it out with some compressed air and it should quiet back down again.