We like to vary the music on the bumper. Just for the hell of it. And
sometimes (often, actually) to match the music in the bumper to the tone of
the episode. We have, I think 4 or 5 variations. Congrats, you're the first
to notice this.

You'll see Walter again this season after "Dust," and I'm trying to work
in one more before the end of the season, but it's tough, given what's been
going on in the latter half of 2260.

jms