Audio desync

So I’ve recently just bought a Samsung S95B, I’m having problems with the audio and video while gaming though. During gameplay it’s fine but when a cutscene starts there is only a small almost unnoticeable delay between the audio play and then the cutscene video playing. But as the cutscene goes on it progressively gets worse and worse until there’s almost what looks like a 2 second delay. Im not using the tv speakers, instead I have my headphones plugged into the pc and I’m using the tv only for video alone but I don’t see how this would cause a problem. I have the tv in game mode, I’ve tried changing both the audio and video settings and everything, I’ve just run out of ideas, any clue what’s happening?