Check where the phono jack meets the pc audio out. There might be an alien karaoke device that was planted there when you were up getting a pepsi from the fridge. If it is there, destroy it immediately - it enables them to intercept your audio output and sing over it with their own insufferably bad vocals, which no one should have to tolerate. This case has been well documented in the past. They tend to like Celene Dion. hehe
No it sounds like you audio bit rate could be dropping. I hear a similar effect when I am listening to my wireless headphones and they start to go out of range.