Yesterday I started GK2 and while watching intro freezing sound drove me nuts (it stopped like for a second and then continued). The game sounds fine, only prologue sound is wrong... Strange.

Are you sure it is just the prologue? I find it surprising.
I remember I had a problem with sound and there is a thread adressing my issue.
http://www.gog.com/en/forum/gabriel_knight_series/gk_2_stuttering_audio_problem