DecoyMusic.com

So I was playing some music about an hour ago, when I realized that, somehow, almost all of my songs got messed up. iTunes will still play the song, but it sounds as though it were passed through some sort of weird filter - certain tones (esp. vocal tones) turn into weird electronic noise. I checked my iPod, and the songs are the same way on that. The really weird thing is, this is affecting songs that I was listening to earlier tonight, and I can't think of anything that I would have done in that timespan to mess up the files (which, btw. are stored on an external harddrive). Have any of you ever heard of anything like this, or know how I might be able to fix it? I'm thinking any recovery will be a long shot, but I'm almost frantic right now. If you know any way to help, it would be much appreciated. I mean, every album I've ever bought was in those files...