When I have my HVAC control to off or "0" air still blows through the vents, the faster I go, the more air blows through. Is this normal for the G6?

Mine does the same so i need to control the hot and cold even when it isnt on...
I know i could just close them but i have an air freshner...???

The numbers only represent the fan speed. Even when set to "0", or fan off, the ventilation system is still physically open.

That's why the faster you go, the more air comes out. The intake is in a relatively high-pressure area (same place they put cowl-induction intakes), so increased vehicle speed generates increased air movement through the vents.

To stop the air completely, you'll have to physically close the system - shut the dash vents.

Simple way to fix it: with the fan off hit the recirculate button. Problem solved.

I haven't tried this but I read somewhere else on similar Malibu that system may go out of recirc mode after 10 minutes by itself if fan switch off.

The problem with recirc mode is that it cycles the AC compressor to prevent from condensation forming in the vents. Doesn't matter if the AC is turned off, it still runs the compressor.

It was like that on the Malibu, and my dealer confirmed that it's that way on all GMs these days.