One possibility I can think of, keep in mind there are still spam files that are around mp3 file size. They might in fact be spam files. This thread will give you an idea of most commonly spammed files: Virus thread: Typical virus spam file sizes - Make a note of them (click on blue link to see)

I'd recommend checking the files to play with VLC - (click on link) which although is fundamentally a video player, can play all the audio type files you will find using LW. If VLC cannot play the songs, then chances are the files are deliberately corrupted spam files.