Speed Dependent Volume Control (Midline System And BOSE System)
WARNING: This page is about a different car, the 2003 Nissan Altima. However, it is still accessible from the selected car via links, so may be relevant.
If activated, the radio output volume will be automatically adjusted to compensate for increased driving noises at higher driving speeds.
The radio receives a vehicle speed signal from the combination meter, and selects the output volume.