Originally Posted by Maxwell
Do the noises change when you rotate the vent directional dial, I'm thinking it might be a flapper valve.
Interesting idea.
It may well have something to do with the A/C controls: I observed that under normal circumstances the red light that indicates that the A/C is working does not come on when the fan is completely shut down, it only comes on when the fan speed is set to at least "1". Same goes for the light that indicates that no air from the outside is used.
Recently though I found the lights flickering when the fan speed was set to "1/2", the first setting above zero. And with the noise the other day the light for the A/C even came on when the fan was shut down completely.
I will observe this further.