GM Service Manual Online
For 1990-2009 cars only

A reminder tone sounds when the headlamps or parking lamps are manually turned on, if the driver's door is open and the ignition is in LOCK/OFF or ACC/ACCESSORY. To turn the tone off, turn the knob all the way counterclockwise.

In the automatic mode, the headlamps turn off once the ignition key is in LOCK/OFF.