Here's the official support page, which I Stumbled! upon a few minutes ago.
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.If my computer behaved in such a manner, I'd automatically assume virus. If I got the Disney version of the unique system notification, I'd blow my brains out with a .410 shotgun revolver. Why wouldn't they choose Chopin's Death March instead? It makes no sense, man. Makes no sense!