2006 Hyundai Sonata Electrical problem?

Have a 2006 Hyundai and whenever the heater fan is on it will occasionally almost stop blowing for about a half second. What I mean by that is it will be blowing smooth and then for a very brief moment almost stop blowing. Headlights also slightly dim when this happens. Any thoughts as to what would cause this? possibilitys would be a problem in the blower motor circuit or maybe the alternator. if the car is still in the 5 yr/60k mile warranty period, it should be covered.Car Repair Talk's forum.