Buzzing noise

I started getting a weird buzzing noise coming from my computer and I'm not sure what it is.

I thought it was the power supply so I installed a new one but the noise will not go away.

Also, I unplugged the harddrive and the noise continues so I know it's not that.

The buzzing sounds like an old tv set or a monitor that isat too high of arefresh rate.

Could also be a dead rat withits tail rubbing against the fan on your video card.