What the heck is this thing. CAn someone explain it to me? There is really nothing in the manual explaining what it is.

I think that is Speed Sensitive Volumn. It increases the radio volume as road speed increases (which causes more noise) You can adjust the level. If you push the Tune/Channel knob it will step through the different audio settings. You can adjust each one as you go through them. Look on page 4-33 in your manual.