screen flashing on and off
 

Hi cam anyone help me i hav a 2003 x5 diesel sport and the screen in the dash flashes on and off on all setting ie tv,satnav,trip computer when it goes off i dont lose any sound and the screen is only off for a second and then comes bac on for about 40 seconds then off a agian and so on and so on i hav swaped the front screen with my mates x5 and its still the same any ideas please

swap nav units in the rear hatch area. see what happens.