My friend had an iPhone 5s crap phone imo. It did have a screen replacement. After dropping it in a life proof case it started flickering at the bottom and got progressively worse to where the edge of the viewing screen raised half and inch and touch wasn't responsive. After reading posts i messed with the phone and was able to stop the flickering, get the bottom of the screen back to the bottom of the display, and got touch back. I'm convinced a cable is tweaked or is touching something it should not due to a bent frame as mentioned in one of the above hypothesis'. But i did was just put my thumb 1/3 from the top on the backside and fingers on one side. Using my other hand and the hand with the thumb in on the backside and fingers on one side i bent the phone inward somewhat it seemed to make the shaking go away the more i did it so now the phone seems perfect aside from where it was dropped. Hope this helps, maybe try pressing your thumb into various areas of the backside and apply some pressure to the edges. It didnt work at first but i kept at it a little and it started to help and completely fixed it after.