Most likely it is the resistor in the blower controller. See if it affects your AC as well. If so, it costs $140 to fix the resistor. This is from personal experience. I told the stealership to shove it back up their exit hole.
Your best bet is to get a working one off eBay for tons cheaper.
2006 Pontiac G6 GT
AIT front bumper, Black Eagle Eye Halo Projectors with DDM Tuning 5000k HIDs 35w,
GT door decals, painted interior trim, red calipers, de-chromed window trim
WAMS tune, CRABS, aftermarket sound system