I was surfing around the net this evening and ran across a funny article in the Microsoft KnowledgeBase.

Did you know that your computer suddenly and randomly playing classical music could be an indication of a hardware problem?

According to the entry at Microsoft:

During normal operation or in Safe mode, your computer may play "Fur Elise" or "It’s a Small, Small World" seemingly at random. This is an indication sent to the PC speaker from the computer’s BIOS that the CPU fan is failing or has failed, or that the power supply voltages have drifted out of tolerance. This is a design feature of a detection circuit and system BIOSes developed by Award/Unicore from 1997 on.

This gives the idea of beep codes a whole new meaning.