Originally posted by Shrike
No, they only have .mp3 as a file type for fun. 
I don't use my MP3 player for CDs.
don't make me look like a fool Shrike, that's not nice when someone's trying to help you. I'm not the one that's asking for help. When someone helps you, you don't act sarcastic.
you said:
My computer is playing MP3s without me having an MP3 player running, or indeed any sign of an active process in my task manager.
My question was how do you know they're MP3s!? For all you know they could be OGG, WMA, MP1s, anything. If it doesn't show you what's playing, you don't know what it could be.
I'll ignore your sarcasm and keep trying to help.
1) Is it playing songs you have on your computer? or music you've never heard before.
2) Do you have a CD in your drive
3) What program is set to play Mp3s by default? what program do you use to play Mp3s (if different from default)
4) What OS