have the service guy check your front tie rods. The G6 seems to have weak ones, as I've had mine replaced twice. Alignment issues and vibration issues ensue from loose tie rods.
Likewise, the type of driving you do will affect tie rod life. I drag raced a lot, hard breaking, and i used to love to cruise the mountain roads in Alaska. My brakes and tie rods suffered hard!
Lastly, as tires wear, they tend to amplify road vibration. And with as much traffic as there is on our roads here in Florida, the roads have permanent "waves" etched into them by heavy trucks, etc. Sometimes it feels like the car is out of alignment, but its just the road.