I use an iPad 2. I just saw a thin vertical line on my iPad yesterday. It appeared underneath the touch screen, it looks like a thin thread. Sometimes the line is black, sometimes it's white depending on the background of whatever I'm viewing. I have restarted the iPad and the line is still there. The line does not affect the touch screen, the iPad responds and works well, but I just don't know the source of the line and how to get it away. Any clue?