Yeah the note is made by the spin speed of the disks being varied as the disk heads are moved towards the centre of the disk. It was first done on Sirius pcs back in the very early 1980s when someone discovered if you varied the spin speed across the disks surface you could get a disk to hold more data The side effect is the drive emits a different tone depending on the speed so to get it to play a tune you need to program a pc to move the disk heads to precise places on the disks surface which is both kewl and hard to do!
There are a lot of other examples with links at the end. A good one is Bohemian Rhapsody being played by a scanner.