Sigh--my 7-month-old 50" GT50, delivered by BB July 2012, has developed an audible-at-10 ft buzz in bright scenes. Prior to this, I could hear a faint buzz a few inches away from the back of the screen, but nothing I considered problematic.
I followed sheshe's link to the ST50 buzz thread (http://www.avsforum.com/t/1444504/needhelp-plasma-buzzing-panasonic-st50-when-is-it-not-acceptabel/60#post_22713731
) and found this interesting post by Donat76:
The buzzing is caused by the coils on the inside of a TV but does not indicate a defective TV in most cases. Coil noise has plagued the graphics card industry for quit a while and Asus uses solid core chokes (coils) instead of open air chokes in their top end graphics card to reduce the vibration. Chokes vibrate all the time. It's just that they can vibrate at an audible frequency when you put a lot of power through them. Compound that with a loose screw and the noise can become louder. Most times they glob some high temperature glue on the coil to quite them down and overtime this glue can deteriorate. I bet if I put a white slide on my TV long enough, I could probably weaken that glue enough to make it buzz louder.
It caught my eye, as the buzzing problem only surfaced about a month ago when I noticed a nasty case of USA logo IR, and ran the Panny IR wipe a few times. Either I had an unlucky coincidence, or the glue may have given out with the extra dose of "white" on my screen. When I first noticed it, it was LOUD, then it subsided after a few minutes. So I've had fingers crossed that it would "take care of itself". After a month, however, that doesn't seem to be the case.
I guess I'll call for service, and see if I get lucky. Sigh
Oh, and I can still see the USA bug in light scenes, but I can live with that.