all of the sudden a couple of the mp3 files are playing back really weirdly. all loud and horrible.

You didn't say whether this was on the car player or on the PC.

If it's on the car player, what is the version of the software running on the car player? There was a known bug in version 2.0 Beta 3 (and possibly 2.0 Beta 7 though I'm not sure) which did this.