I was driving along tonight with the ventilation system set to fan speed 4, set to cool, only the middle slider over (blow air at you, not feet). All of a sudden, I hear a huge "CRACK" noise and then the fan stopped blowing! I turned off the blower and then put it back on; it started back up but it sounded quieter than normal, and it made weird noises when set to 3 or 4 position (some kind of buzzing). What on earth could this be?!?! The fan still works, and after the incident, I turned it off and on a couple of times and eventually the noise went away when turned to 4. Is this the sound of imminent failure?