If your Plasma TV makes a buzzing sound when it is turned on, this is normal. It's caused by the electrical charges that are used to power the pixels that create the images on the screen. The buzzing, however, should not be so loud that you can hear it when the volume on the TV is set at normal levels.
If your Plasma TV is buzzing loudly, follow these steps:
Set the volume of the TV to the setting you normally use.
Stand 10-15 feet away. Perform a sound test...