interesting info. I'll look into the exact settings for my TV. And in the meantime, no sooner (an hour or so later) had I replied to the forum that I'd figured out the problem, I ran into a very similar but slightly different problem.
The music album art, transitioning backdrops, everything looked great after returning the resolution of graphics on PC back to 1920 x 1080. But then I went into Photos, and tried a slide show of some pics from my Nikon digital SLR, and saw very similar distortion of photos! Did not see it in photo album view, but once in slide show, it would either show the picture OK, or briefly show it OK (1-2 seconds) then it would distort similar to what I described earlier on the original problem. Very confused, especially since some photos would show OK, then when I restarted slideshow to try again - a different set of photos would show the problem.
I can't help but think this must be a graphics issue on my PC, but don't understand why it doesn't happen all the time for all images? And why it can and does display some pics OK, but only momentarily - then shows them with the angular distortion. Any ideas?