High-frequency buzzing is a problem inherent to all plasma TV technology. Even if you buy a top-of-the-line plasma, you might hear a high-frequency buzz if you're seated close enough. If the buzzing is loud and unbearable, it could be a defect in the TV. If it's almost tolerable, however, there are a couple of things you can do to reduce the problem.
Change the power-consumption settings on your plasma. Using the remote, enter the main menu and look for power-control options. Find a setting that uses less energy (like "Power Save" or something similar). Although it might slightly reduce the brightness of the picture at times, this can significantly reduce the buzzing.
Turn down the brightness and/or contrast. Displaying bright content onscreen can sometimes make buzzing more noticeable.
Change seating positions. Plasma buzzing is often not detectable when sitting farther away or off-centre. Experiment with different seating positions until the buzz is less noticeable.
Replace the TV set. When all else fails, return the plasma TV to the store and exchange it. Plug in the new TV while in the store, if possible, to examine the extent of the buzzing.
Buzzing is caused by high-frequency vibrations related to electronic discharge. Most of the time it is only noticeable when very close to the screen or viewing behind it. All plasma sets buzz to some extent. It is usually not detectable by everyone or over normal television volume. Even different sets of the same model can sometimes buzz differently.