David Fincher chose The Dust Brothers to score Fight Club even though the trippy electric music duo had never done a film score before. In fact, he may have picked them because of their inexperience, to bring a fresh perspective to the film. After all, a film that plays around with identity and point of view needs a unique soundtrack.
The Dust Brothers, a.k.a. Mike Simpson and John King, worked as music producers, producing Beck's album Odelay and the song "MMMBop." (But that doesn't mean you can hit Hanson as hard as you can, no matter how much you might want to.)
The Dust Brothers have never produced an album of original music. They stress, "Fight Club is not a Dust Brothers album, it's a Fight Club album." The movie is unique, and so is its music. (Source)