Center sound fluctuates and is unstable.

If the center sound fluctuates and is unstable, change Sound mode to Music, and change Surround Effect to 0.
Follow the steps below to change the settings.

Sound mode

1.  Press the HOME button on the remote control.
2.  Select  Settings.
3.  Select Sound in the TV category.
4.  Select Sound.
5.  Select Sound Mode.
6.  Select Music, then press the Enter button.

Surround Effect

1.  Press the HOME button on the remote control.
2.  Select  Settings.
3.  Select Sound in the TV category.
4.  Select Sound.
5.  Select Advanced Settings
6.  Select Sound Mode Related Settings.
7.  Select Surround Effect and set to 0. 

NOTE: This TV uses an upmix process from 2ch to 3ch to make center sound from stereo sound.
For this reason, center sound seems to be unstable depending on the content.
When Sound mode is set to Music and Surround Effect is set to 0, center sound is disabled and the sound will be stable.