I think my speakers are going bad. Lately they've been making a buzzing noise, even when there is no sound coming from them. Plus, I think they are interfering with my monitor. I see scan lines going up the screen, and this is an LCD monitor, mind you.
Either that or your sound card is going bad. If you have another set of speakers, try connecting them and see what happens. If the buzzing stops you know its the speakers, which would obviously be the best case scenario.
These speakers are 8 years old, but I'll dig out another set of speakers just to be sure. Would it make a difference if it is onboard sound on the motherboard?
Also, whenever I turn off the speakers, the monitor turns off and then turns back on.

Edit 2: I remember I had these speakers set up on another computer a few years ago, and whenever I moved the mouse, I heard a loud buzzing sound come through the speakers.