Hey, I answered my own questions, it looks like I need a remote to do this. Fortunately I have a Logitech Harmony 650 that I programmed and was able to go through the menus.
Sync Options -> H-PLL Post-Coast -> 1 lines
did the trick. (was set at 0) No more flickering! The other suggestion referring to the 480p-in settings did not stop the flickering.
Edit, thanks for the answer harrumph, I was typing this message while you answered and I did not see it until I posted.