It could be a lot of things, but my experiences point to one or more plastic fasteners that have broken or come loose, and slight vehicle vibration causes a "ticking" sound. Sometimes it can be the retainers on the cabin filter cover, easy to check ?

Are those the only conditions under which it happens ? When you turn off the AC, does the noise slow down and stop, or does it just keep making noise, then suddenly stop ?

Does it happen when you run the heater, then turn it off and open the door ?

If the noise only happens when the pressure releases and the AC fan slows down/stops, I think either the fan is hitting a slight obstruction when it slows down, or some foreign material is inside the AC piping that flutters when fan pressure is reduced.

Can you ask one of your parents to try these tests with engine NOT running (turn ignition on but don't start engine), and let me know what you hear?

AC on, doors closed, turn off AC. Any noise ?

AC on, leave it on, open door. Any noise ?

AC on, turn it off and open door at same time. Any noise ?

With the engine not running, if it still happens, it's an AC fan or air piping issue.

With the engine not running, and if it doesn't happen at all, it's probably not an AC issue, but maybe an engine, transmission, or powered accessory (like alternator or water pump) issue.

Also, the Chevrolet has really good sound insulation, and with the doors and windows closed, outside noise (and engine noise) gets a lot quieter. In opening the door, the sound level will return to normal and you may simply be hearing a non-AC issue that was masked/muted with the door closed. But this is just a hypothesis.

Please understand, it's difficult to do troubleshooting on a possibly complex issue by writing comments in a forum, so bear with me because I could be going in the right direction, but I might also be wrong.

Try the above and let me know what happens, OK.