Hi!

If you know what you're doing inside a TV set, or at least know what to stay
away from, then open it up and have a look. Try disconnecting the speakers
and seeing if the noise goes away.

It is possible that the noise is not coming from the speakers. Some cheaply
designed/defective/overloaded power supplies can make noise when operating.
Since your TV is probably a fairly modern unit, the low voltage power supply
probably runs all the time...and that's why you hear the noise.

If it is power supply noise and nothing seems to be wrong with the set, it
may just be something that the TV will have throughout its useful life.

William