I hear noise in all the channels
When you hear noise while watching TV, you can have a Sound Test to see if the test sound is played clearly.
If there is no noise during the Sound Test, it may be due to poor reception on the TV or poor connection of
peripheral (set-top box, game console, DVD, blueray player, or PC). You are suggested to check the connection.
If there is noise on a particular channel, it is caused by unstable reception so you are suggested to have an inspection by the broadcaster you are subscribing.
How to fix
Smart TV ‘12~’13
[Smart] or [Setting Menu] → [Setting] → [Support] → [Sound Test]
webOS TV after ‘14
[HOME] → [SETTINGS] → [ADVANCED SETTINGS] → [SOUND] → [Sound Test]