I got the EXACT same melodic noise today off my Maxtor 120 gig 8 mb fluid bearing drive when it 'disappeared' from my system today. I run XP Pro, have a Gigabyte 7vrxp and used the drive as a slave for an ftp. The bios will not detect it. The drive is two weeks old.
It DEFINITELY is coming from the drive and is not a post code. Never heard anything like it from a pc. It sounds more like a ringer from a childs play cellphone.