Ok, if it comes in gradually and regularly, it's not a pixel mapping issue. Assuming you've a DVR, do these lines stay still or continue moving when you pause the DVR? I'm assuming that, if it is an issue related to a mechanically distorted image, that the lines would continue to move (since processing continues to occur despite the DVR being paused). If the line pauses, the issue may be elsewhere. Either way, this certainly sounds like an issue you should bring to the attention of Calibre support, in case your unit is faulty.