My computer began to emit a high pitched whine recently. I wasn't sure which component it was coming from, and it persisted even when I had shut the computer down. The only way I could get it to stop was to physically shut down the power supply (via the switch on the back). This leads me to think the power supply is the culprit, but I'm not sure why it's making this noise. Is it a sign that it's dying? I wanted to be sure before I replaced it. Any thoughts?