No music playing, so I don't believe that's it.
Neo's link does look very similar. Yes, there is a BIOS update available. Maybe it is time...
The only change recently has been the addition of a Deskjet 895Cxi printer, sharing the parallel port with a ZIP drive. Hmmm.. the ZIP was there first. Leaving the printer on when I attempt to shutdown sometimes is a problem. These are the only apparent symptoms. I ran system file checker and found nothing wrong.
The mobo is an ASUS CUSL-2C. I'll check the info on BIOS upgrades.
Edit: I went ahead and updated the BIOS (I'm getting nearly fearless with this BIOS updatin' thing

). So far, so good, we'll see if it helps.