it occurs all the time from what i've gathered. it's in pc mode and i've tried an hdmi cable that works fine without the artifacts on other hdtv's as well as a vga cable that has no artifacts on other hdtv's but when used on my hdtv the artifacts appear.
i've also tried multiple video cards on my pc to see if that was it and it's completely the tv. it can't be the hdmi or vga cable and it can't be my video cards, it's the tv.
also the tv has a long vertical band on the right side of my screen about an inch and a half wide that is darker than the rest of the display. it isn't very noticeable but in the section colors and lighting is definitely just a few shades darker. i also have this appearing now sort of in small areas in the middle of my screen that's almost like a ghosted image. this is not a plasma screen btw so i have no idea what's up with the ghosting as it's lcd and only about 4 years old and kept in perfect condition.