3 Things.
1 Flashing on/off could be radio loosing power, so check for loose connections behind the radio, usually loose red or yellow wires.
2 If by flashing you mean going lighter then darker then look also for loose dash illumination wire (orange behind the radio.)
3 If 1 or 2 don't solve the problem then try turning off the auto dimmer feature in the menu and see if this helps. Alpine say,
"If your vehicle should have a dimmer control for the dashboard lighting, never connect the DIMMER cable (orange wire behind radio) of the radio to this dimmer control"
The radio is probably reading a reduced voltage on the dash illumination wire which is just at the programmed threshold and can't decide if the lights are on or not so keeps dimming its display then brightening it. Three ways to fix this is to turn off auto dimmer feature in radio settings, try turning up the dash illumination on the controller, or disconnect the orange wire behind the radio.
Hope this helps.