I used to see it all the time, not so much anymore. Get used to seeing the lines (unless it's under warranty). If you take the LCD out, you may be able to pinch the edges until you find where it needs to be pinched to keep the lines from appearing. Then you can place something behind the LCD to keep pressure on that point and hopefully the lines will not appear. Be careful though, you will be putting pressure on an expensive piece of glass.
I got lucky and am not sure if this is what fixed it, but I had a laptop with a horizontal line and couldn't get it to go away. I found a adjusting screw on the backside. Most of these that I have come across seemed to let me increase the brightness though now that I have thought about it, that isn't possible as the backlight only interfaces with the FL inverter. At the time I thought I would see if I could increase the brightness by turning the knob. My line didn't show up on black and I was in DOS to see if the letters would get brighter. Nothing noticable happened so I put it back together and lo-and-behold, the line was gone. Fluke, maybe?