iPhone 4 is OFF, every 5 minutes and 30 seconds the White Apple shows on screen for 3 seconds, then screen goes black again, then 5 and half minutes later the Apple Logo shows for 3 seconds. This repeats continuously. The iPhone is definitely OFF, buttons do not function, call iPhone no response, it is OFF. When powered ON and screen is locked the screen remains black and iPhone works fine. The every 5 minute 30 second White Apple does not appear until the iPhone is OFF. Any explanations?