I recently bought a Roku Ultra, and have an older HD TV, Hitachi 42 inch model LE42S605, together with a Samsung blu-ray home theater model HT-E5400. I originally had the Roku as input into the home theater, with output from the home theater to the TV. I kept getting green or black screen flashes every 3 to 5 minutes, and the TV would act as if the signal was lost and show "Detecting" on the screen for a few seconds and then the screen comes back. Audio was always there, never stopped. This happened whether or not I was streaming - even on the Roku home screen. After researching my TV and home theater, I realized I could wire it up using Audio Return Channel (ARC) and connected the Roku direct to the TV, then TV to home theater thru ARC. No problems ever since. Thought I would share the solution in case others have experienced similar and this might work for them.
Thanks, it seems that the issue is the receiver HDMI version. I have a wonderful Samsung HDMI receiver, that is now obsolete, as it has HDMI 1.4 rather than 2.x the ROKU device should have downgraded its signal to match my equipment, not me having to buy another receiver.