I just received a new 60ST50 on Monday and have ran into the buzzing issue. I've got about 25 hours on the TV at this point (around 4 hours of blu-ray, 2 hours gaming, the rest has been running D-nice prep slides). I sit between 8 and 9 feet from the TV. In silence (the only noise-making object being a refrigerator in the next room) from my seat I can hear the buzzing on the Red / Green slides, the Blue slide buzzes but is very low, and the white slides of course buzz VERY loudly - I can even hear it from the next room faintly. If I run the anti-IR scrolling bar, the buzzing actually follows the white bar - the left size of the TV buzzes at first, and then the center and the right side as the white bar moves.
During the 2 hours of gaming I did, I played Journey (PS3) and Tales of Vesperia (Xbox). Journey tends to be a bright game, and I could faintly hear the buzzing OVER the sound / music of the game. In Tales of Vesperia, I could hear the buzzing over the sound in the Menu screen.
Has anyone had buzzing DECREASE once they reach the ~100 break-in period? It sounds like my set is still on the "lower" scale of buzzing, but I know it's there and it annoys me as I can hear it during quiet / low volume scenes. It's a October 2012 model with a -2 at the end of the model number, and it looks like the screws have washers when I use a flashlight to look inside the unit.
It was purchased from Amazon, so I still have a couple of weeks to decide if I want to start the panel exchange game :\ Besides the buzzing, the set seems great - I haven't noticed any dithering or other quality issues. I'd hate to exchange and get a unit that has more problems.