Samsung UN46ES7500F E-Manual page 590

Plasma TV is making humming noise.
Plasma TVs typically make
for PDP TV
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
back of your Plasma TV is too close to