Allow volume control of warning tones

Purchased a 2013 Fusion Titanium.  The backup (and other) warning sounds are more of a musical tone as opposed to the older style "beep".  The volume is low enough that I cannot hear it, rendering it useless.  If the user could adjust the volume that would make the system useful again.  Set the minimum volume to what the default is now so that people can't turn it down to the point where it is effectively off.
Curran F 12/11/2013
My 2013 Fusion lowers the radio volume once put in reverse.