You can hear a slight noise from the TV speakers (only models with TV center speaker mode).

Models with TV center speaker mode have a CENTER SPEAKER IN terminal or S-CENTER SPEAKER IN​ terminal in the back.

If an AV receiver is not connected to the CENTER SPEAKER IN terminal on the TV, or if an audio system that supports the S-CENTER SPEAKER IN​ terminal is not connected, you may hear a slight noise from the TV speakers when [Speakers] is set to [Audio system].

If you are concerned about the noise, disable the following setting:

Press the HOME button, then select:
[Settings] — [TV center speaker mode] in [Display & Sound] — [Audio output].