Greetings. My second PN63C7000 does not buzz as loudly as my first.
With both sets I used an iPhone decibel meter app to measure sound levels in the 'cone of buzz' from the exact same location and with ambient sound levels being the same (though it was days apart). Both sets were tested with the 'check signal cable' screen after being run for 10 minutes with HD antenna content. The first set had about 40 hours on it, the second, about 24.
The first set, when powered on, resulted in a consistent jump of 9dB from 39dB to 48dB. The second set saw a 5dB jump from 39dB to 44dB.
Not exactly scientific, but the numbers do corroborate my impression that the new TV has a less noticeable, and therefore less annoying, buzz.
Now, if only my new panel didn't have an abnormally bright 1" horizontal band running across the top of it... sigh