It also happens even when the sound itself is muted. It's mostly noticeable when there's not much happening sound-wise, e.g. I can also hear some interference when I minimise and maximise things in Windows. The buzzing only seems to happen when doing certain things, possibly when there's a heavy hard disk and CPU load - I can hear it when watching HD videos from the hard disk and while playing certain games. I'm using the built-in Realtek HD audio on my Gigabyte P35C-DS3R board, and my headphones are a pair of Audio-Technica ATH-ANC7s.
Lately, I've been hearing an annoying buzzing noise when using my headphones.
