all plasmas buzz, some worse than others, although samsung is known for consistently producing sets that have a tendency to buzz pretty loud. It';s basically a roulette and I wouldn't call your TV defective.
ht Panasonic 60" ZT60, Monitor Audio: Silver RX6, RX Centre, Silver RX1; Martinlogan Dynamo 700, Marantz SR5006, PS3, Oppo BDP-103D
2ch Sony KDL-32W650A, Sonus faber Toy Monitor, REL T3, Marantz PM8004, Sony BDP-S1000ES, JVC T-X3 tuner, Apple TV, Peachtree Audio DAC•iT, Sennheiser HD598
pc Monitor Audio Radius 90HD, Audioengine D1, FiiO A1