Loud bang when switching between vent modes...

[DRM500RUBYZR-1]

IF:
Nothing has been disturbed or come loose, and is being buffeted by airflow,
then; there are only really two movable features within the system.

1- the diverter valve and actuator- this does exactly as it sounds like it would, i.e. it diverts the airflow to the outlets invoked by the selection made through the control head, then said selection is passed to the programmer to execute the command, then on to the actuator and the valve, which then re-directs the air.

2- the blend door aka the air mix door- again does what it says, i.e. mixes the ambient air with heated or cooled air to deliver it and achieve the temperature requested at the control head. Temp selection is made at the control head, then communicated through the programmer, which instructs the blend door actuator to move the door to a position that will yield the best mix of air to obtain and maintain the selected temp.

You must determine which sequence is in process when you hear the noise.

I suspect the blend door actuator.

When the car is first started, the system cycles the blend door from fully closed to fully open, one time.
This process conveys info back to the programmer so that ot knows the travel possibilities of the door aiding in determining the soon to be requested commands.

It would seem to be either sticking, or unable to hold itself open, and slamming shut, which although it can operate, it does not have enough strength to hold the door fully open.

While I am sure there are electronic testing procedures in the FSM, it would be far more valuable for you to evaluate the operation of both variables of each system, and determine what is requested immediately before you hear the noise.

Hope I have helped.

Marty