Okay, I have searching on the net for a week, and found some posts about this problem (not specifically with LG TVs). All solutions said, that set digital output mode to PCM. It works for me as well, but in that case no Dolby Digital 5.1 . Also, an LG tech called me, he wants to replace the main board of the TV, but I don't think that will help (he isn't sure as well). If that is a hardware issue, than I should get this problem via PCM setting as well (moreover the sound is digital, so the two options are sound or no sound, digital sound can't have interference, popping noise or things like that). So assume this is a transcoding issue, and it has to be the software.
Anyone experiencing a thing like this?