I've had this problem for quite some time now. I've seen a few other posts of people describing my exact issue before too. You easily see it in the dark when you change the TV to an empty input. Of course the whole screen is black, but there's slightly brighter than black horizontal bars in the center a few inches high and about the width of the screen flashing on and off. Very annoying and visible in dark scenes. It's not a floating black issue, as I have that too and know it's different.
Has anyone had a service tech able to fix this? I finally filled out a viera service request this morning and got a case number for an onsite tech. But now I realize my warranty is out by 7 months (you only get 1 year, right?), and will most likely be charged for labor and parts if anything gets replaced. I purchased my S2 in Nov of 2010. I also mentioned in my trouble ticket about my floating blacks, but after revisiting some threads here I realized floating blacks are inherent to Panasonic plasmas and can't be repaired with a new part.
But if I let this onsite service continue, it sure would be nice if the flashing bars could be repaired. Also, anyone have any clues how much cost average labor would be for the Panasonic tech onsite?