Here is what the owners manual says about the Bose premium system. pg3-71
If your vehicle is equipped with Bose the system will
have AudioPilot® noise compensation technology.
AudioPilot monitors the level of noise in the vehicle and
automatically increases or decreases the level of the
audio to keep your audio above the noise.
To use this feature set the volume at the desires level.
Press the AUTO VOL button until AVOL appears on
the display. This feature works best at lower volume
settings where background noise may be louder than the
audio.
At high volume settings, where the audio is
much louder than the background noise, there will be no
change in the audio level. To turn automatic volume
off, press the AUTO VOL button until AVOL OFF
appears on the display.
This is what Bose has to say about it.