The off road transition menu is hidden, from the Routes page (NB not the Setup Routing page) use the left or 'menu' key, select Off Road Transition and then you have options for Auto (default, usually works OK), Manual (you don't want that) or Distance (set a distance of choice to bleep before a transition).
None of this actually turns beeps on and off (that's in the Setup Tones menu) or backlight (that won't come on unless you first switch it on manualy - NB you have to do this every time you turn the GPS on and you want backlit prompts).
