Try the following:
1) Open ‘Audio Settings’
Go to ‘Settings’ by scrolling down the main menu from ‘Home’.
In Settings, scroll down to reach ‘Audio’ settings, and select it. The Audio Settings screen will open.
2) Select ‘Audio Mode’
Use your remote to scroll down to the 'Audio Mode' option in the 'Audio Settings'. There are two options available here, 'Stereo' and 'Auto'. Choose the Stereo option using the trackpad on your remote, and select it. This should stop any error in audio selection.
3) Select ‘HDMI’
Select the ‘HDMI settings’ from the ‘Audio’ menu, using the remote trackpad. You can change the HDMI option from ‘Auto’ to ‘PCM -Stereo’ or ‘Dolby D/D+’. Select PCM-Stereo.
Hopefully dialogues should be audible now.
Note:
It is advisable to select the output as Dolby Digital only when we connect a home theater as an output to the TV. Because, for Dolby audio, the app (or even a DVD Player) might output Compressed Audio, that plays well only in Home Theaters with different speakers. The TV's speakers cannot reproduce the same effect because they only have 2 stereo speakers. In your case, the dialogues might be output to the FRONT-CENTER speaker of a home theater, which the TV clearly does not have. Hence, the TV might be reproducing only the audio from the FRONT-RIGHT and FRONT-LEFT speakers of a home theater, which in this case could be the background music you are hearing. Long story short, it is advisable to NOT select DOLBY DIGITAL or COMPRESSED as the audio output type in our TV's settings when we are using just the TV for listening the audio. If we do,
1) The speakers might not reproduce some of the sounds from the audio output.
2) There could be sudden and uneven increase/decrease in sounds during different times when a movie is running. For example, a bomb explosion sound could be too loud. Or dialogues could sound too low.
