From my 2006 Owner's Manual:
AUTOn(Automatic Volume): With automatic
volume, the audio system will adjust automatically to
make up for road and wind noise as you drive, by
increasing the volume as vehicle speed increases.
Set the volume at the desired level. Press this button to
select AUTO VOLUME MIN, AUTO VOLUME MED,
or AUTO VOLUME MAX. Each higher setting will
provide more volume compensation at faster vehicle
speeds. To turn automatic volume off, press this button
until AUTO VOLUME OFF appears on the display.
From my 2009 Owner's Manual:
Speed Compensated Volume (SCV): Radios with
Speed Compensated Volume (SCV) automatically
adjusts the radio volume to compensate for road and
wind noise as the vehicle speeds up or slows down.
The volume level should be consistent while driving.
To activate SCV:
1. Set the radio volume to the desired level.
2. Press the MENU button to display the radio
setup menu.
3. Press the pushbutton under the AUTO VOLUM
(automatic volume) label on the radio displays.
4. Press the pushbutton under the desired Speed
Compensated Volume setting (OFF, Low, Med,
or High) to select the level of radio volume
compensation. The display times out after
approximately 10 seconds. Each higher setting
increases the audio volume to compensate for faster
vehicle speeds.