I've had my 50GT30 for around 3 months and the fan noise is pretty bad. It sounds like a twin engine plane about to take off with the engines going at slightly different speeds, kind of a throbbing sound, which is highly intrusive even from 10ft away with my surround system turned up. I can't hear the fans over louder passages, but they're always audible over dialogue. I might also describe them as sounding a bit like the washing machine doing it's spin cycle in the kitchen and being audible through the door.
I contacted Panasonic who recommended that I call out a service engineer (which may have been a standard response to any fault report as I did it through email). I haven't done so yet and am slightly wary of being told that I can't expect the fans to be silent. I don't expect them to be silent, but my old Panasonic 42" plasma panel, which I still have, had three fans and they were inaudible. The only time I would notice them was in a silent room with the TV sound turned down, then if I turned off the TV I could hear the very gentle purring of the fans stopping.
Not sure what to do but I need to do something as the fans spoil watching the TV for me.