FADE Control (Uplevel Radio)
WARNING: This page is about a different car, the 2002 Buick Regal and 2002 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
Push the FADE Control knob to release it. Rotate the knob to move sound between the front and the rear speakers. Push the knob back in to store it when not adjusting.