Like a lot of writers, the right song can get my imagination all spun up. There's a feeling in certain music that just works, and most of my stories have that one song that soundtracks the whole thing.
For example, I wrote a two-book series that hasn't yet been published, but it's about a racing family. To this day, when I hear Tobymac's "Ignition," I get pumped to work on that story all over again.
In published novels, Freefall's song came after I'd finished the book, when I was revising. There's a ninties Def Leppard song, "Two Steps Behind." I could totally see Shane in that song.