On my 42" Pioneer Plasma (PDP-4271) I get the buzz, but I find that the buzzing increases and decreases in volume based on how much "WHITE" is on the screen. If the screen is very bright, or WHITE, I hear a lot of buzzing, but durring darker scenes the buzzing is almost non-existent.
I always figured that was a function of the plasma cells charging being hot (i.e. bright).
At least that's what I thought was the case.
-Adam