It happened with the old 100 lb. Sonys that were in this 2006 coach originally.
It happens on the LG flat screen I put in the bedroom last year and it happens with the Hitachi that I placed above the dash this year.
I haven't gotten any information from neighbors that sounded definitive.
It seems to happen on every channel and every time we are hooked up to cable. Directv and OTA work perfectly. The picture is good but it cuts off the edges, for example the temperature box in the bottom corner on a weather forecast.
This is why I'm scratching my head.