You said it: weird. Try looking the info's of one of the .xml files (Macs-> Get Info; Windoze->No Idea). Does it still recognise the files as .xml (probably yes)?
Also, IMO, the .xml files are actually your .mp3s that somehow (uh, ghosts maybe?) got changed into this .xml format.
Appaently, from what I see in fileext.com, xml files are "eXtensible Markup Language files" and are designed to replace html (maybe try opening them in your web browser???
)
No, I have no idea what kind of application might be responsible for turning .mp3s to .xmls (what's the use?), so you might wanna check your applications, see if there's a "suspect"....