we took the P50G20 back to best buy and the guy from their TV department that came up to make sure it was okay to return said they all do that and especially when they are showing bright images on the screen. Not that his word is gospel but I'm sure they hear a lot of buzzing complaints.
I didn't bother mentioning that it didn't buzz till after the software update, which still makes no sense to me. I was just happy to have my money back and be heading to get lunch.
We replaced it with a Samsung PN50C7000 from a different store and it too buzzes but it is more of a constant buzz. It is far from being as loud as the Panny was when bright images were on the screen and yet louder than the Panny was at it's quietest. Kindof a middle ground between the two but constant rather than fluctiation with what is on the screen.
To me I find this less annoying because it is easier to get used to and tune out. When someone would come on screen wearing a white shirt the panasonic would announce it with a louder buzz which would make it much more noticeable to me.
Neither seem to buzz in the store but my house is much quieter than a store. Heck, I thought our office at work was reasonably quiet till the power went out and all the electronics shut down so I'm sure there is a ton of noise in a Sears or Best Buy, that I don't even realize is there, drowning out the buzz. The Tivo shows up Tuesday so I figure the fan in it will help cover the buzz
Watching regular shows or movies I never hear it with either TV but when watching news type programs it is more noticable but still not bad.
With a price match and another added discount that they just gave me for the heck of it the Samsung ended up only being about $150 more than the panasonic so I'm happy. I'll take a bit of noise in exchange for an incredible picture.