Strange noise in K5

When I review pictures on the LCD screen on my K5, sometimes there is a strange whirring sound coming from inside the camera, which stops as soon as I switch back to picture-taking mode. It only seems to happen with auto-focus lenses mounted on the camera, so I am guessing it is something to do with the AF. Any ideas anyone? Also, I had grey lines on the LCD when I switched it on yesterday, which disappeared after switching it off and on again. That has only happened the once.