Navigation / Radio Performing Erratically

[Skyline]

The Navigation Radio in my 2008 X5 4.8i (it has the upgraded radio) has started doing all sorts of funny things. It will freeze, reboot, have disk read errors, (disk is brand new from dealer). The other day, the Nav map was over the top of the main control screen and frozen there (but following the map). No buttons or turning off the car could take away the map. Until I put the car in reverse, then the camera came up and everything was normal. Yesterday, I could not control the volume of the radio...then the system re-booted by itself and everything was fine again.

Any ideas what to look for here?