I have the same issue with an LG 49UF770V.
I have had this TV for about 9 months with no problems until the last few days, now I get exactly
as you describe, sound drop-outs of up to a half second (occasionally longer) at random intervals,
probably a dozen times in a hour.
System comprises:
Humax satelite PVR connected via HDMI.
Satelite LNB connected directly to the TV LNB input.
Network connected via wi-fi to TV.
Sony audio amplifier connected to optical output of TV.
I see the same issue using any input method so my conclusion is that this must be a
TV software/hardware problem maybe related to processor loading or lack of memory or
both.
As a test I switched the network connection from wi-fi to hard wired, thinking that this may reduce
the processor load slightly, and I also switched the audio out from 'Auto' to Dolby Plus.
Today I watched a full length film on Netflix without any drop-out, and this evening my wife watched
TV using the Humax and only noticed two drop-outs all evening.
Note that no internet was being used by the system this evening other than whatever the set may be
doing in the background.
There have been no firmware updates (unless there is a bug that allows them when the auto-update is set
to OFF).
My firmware version is 04.25.55 (Anyone know when this was released?)
and the WebOS version is 2.21-1341