Hi Miira,
There have been very few reports of a similar problem. We do not have a sure solution for this but there are some things that helped in other cases:
– Verify the integrity of the game files through Steam: Load Steam. From the Library section, right-click on the game and select “Properties” from the menu. Select the “Local Files” tab and click the “Verify integrity of game cache…” button. Steam will verify the game’s files – this process may take several minutes.
– Unplug your headphones (which are you using, if any?) and use speakers, see if the problme persists with a different audio output device.
– De-activate the latest DLC, launch the game and close it and re-activate it through Steam.