I have an 07 G6 GT and after I shut off the car and came outside 20 minutes later I heard a loud blower-type noise coming from the cowl area. I know cars in general have fans and things of that nature that occasionally turn on once the car is off. But then I got into the car and found out that warm air (outside temperature) was blowing through the vents at near full fan speed (all the HVAC controls were in the off position). Is this normal? I just had the head unit replaced by Pontiac under warranty recently so maybe they could of messed something up?