Photoshopeth

I've noticed that my 04 GT, makes a strange noise for about a minute or two that sounds like the fizzing of pop in a can behind the radio/center ac vents whenever the car is switched to outside A/C or vent, but never with max a/c. I hear it louder when I pop the glove box open.

It cools just fine, but my 00 v6 never sounded like that, just curious what it could be.

cliffyk

The HVAC air control valves ("flappers") are operated by vacuum motors, the dash control activates them as required to meet the characteristics you select. What you describe sounds like a vacuum leak, or moisture in the vacuum control system...

Here is how it all works along with diagnostic procedures...

Photoshopeth

Thanks! if it is a vacuum leak then it will probably explain why I've also heard a hissing noise at idle/low speed, I always thought it was from the hydroboost.