XP is playing an unidentified audio file?

Are you on a network? If so, someone could have playfully "hacked" into your system to play sounds, open the cd tray, etc... If not, then you might have a little known virus or worm running on you pc. Try starting up your pc in safe mode, before you get the windows boot screen press F8 and boot into safe mode with networking. If you dont hear anything anymore, then its time to give that pc either a virus clean, or an OS install.