My new 55" also buzzes significantly. The buzz varies and is proportionate to the brightness level on screen and can be heard from 10+ feet away over low-mid volume content.
It's a deal breaker for me, but I'm not sure if I should take my chances and re-order from Amazon or look for an alternative. (Others have suggested contacting Panasonic for possible quick fix...) I'm wondering what percentage of ST50s suffer from this?
For reference, I've aged the panel 100+ hours and calibrated per DNICE's suggested settings.