I just read a Samsung manual that writes it will flicker in Game mode. Ask Samsung (1800SAMSUNG) if you missed that in the manual.
There are other reasons as well.
About TV content. What a mess. As Samsung does not supply the video content, all bets are off.
My tv flickers when TV changes from HD to comercials. The TV also flickers when it is in PC mode. I was thinking about changing the Mian Board will this fix the problem