Audio is especially sensitive. In order for you to hear music from your speakers, data needs to be delivered to your audio hardware approximately every 10 milliseconds, or 30 times in the blink of an eye! The challenge is that your PC is usually doing a lot of other things at the same time you’re listening to music, such as streaming that YouTube video or downloading that new song, and many of these other tasks have complex timing requirements as well. Telemetry infrastructure built into Windows 7 (download) shows approximately 80% of sessions showed no glitching at all, but 4.3% showed 10 or more glitches, which indicates that audio glitching affects a significant number of users.
Full Article: E7 Blog