Mute the cdrom inputs, modem inputs, line-in, etc. if you're not using them. They take an analog signal and hence will pick up electrical noise from inside your computer. After doing this it should go away. Even the port that I do use (line-in for my tv tuner) I keep muted and then unmute when I want to use it so that I can avoid that annoying little sound (happens even on my SB Live!). I can't believe these people have never had this happen before.