I got the 60" 8500 delivered a couple weeks ago, and it buzzes. Heavy. Noticeable even above normal volume, except during big action sequences. Strangely, it is only audible when sitting directly in front of the unit. Move a couple feet off to either side and the sound is gone.
We started a ticket with Samsung On Friday, got a call from them Saturday. After assuring them that I had read and used their online troubleshooting guide, they arranged to have a tech come out to hopefully fix it. Today, the tech company called. I talked with the gentleman for about 5 minutes, but as able to gather that the buzzing sound is common, but "usually" fixable. He was ordering a specific part for the tech to replace.
They should be be out later this week to take a look. I am pretty happy with the response so far from Samsung.
By the way, I had the 60" ST50 before this unit (The kids threw something at it. Smashed the panel). I like the picture of the 8500 so much more (of course it was more expensive, to be fair). Seems to be much more colorful yet the blacks are fantastic. The added brightness works a lot better in our area as well.
Hope that helps in some way.