external monitor grainy/noise display

[cinek]

I got a 13" 2011 macbook pro. I'm using a dell u2711 as my external monitor. I connected it with the dual dvi adapter from apple. Everything is fine, untill (if it's running on battery) the display gets turned off (when I don't use it for X mins). After it comes back up, it's fine for about 2 or 3 seconds, then the image is grainy. To get it back to normal, I need to reconnect the adapter or let the monitor turn off again, and back on. Any ideas what's wrong? I've heard that quite a few people have this problem.....