This problem is being caused by some loose gap on the back of the screen, to solve this problem, you need to make sure the screen is well secured. To do so, just open the back cover and unscrew the battery cover, then stick some very thin foam over ( & around the edge of the motherboard ), make sure these are not covering the camera, volume button etc .. then screw back the cover gently. This should solve the problem!... if still not fixed fully stick some of the same thin foam under battery which isolates the battery from the screen and fixes the screen and problem should go away!