Samsung PN51E550 E-Manual page 29

For details, refer to the Feature.
Plas a
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hu_ing
Plasma TVs typically make
a soft humming sound. This is normal.
It's caused by the electrical charges
that are used to create the images on
the screen.
If the humming sound is loud, you may
have set the brightness on the TV too
high. Try setting the brightness lower.
You can also have loud humming if the