ZIP DRIVE CLICK OF DETH (aka jwgh) describes the circumstances surrounding this song:

Kibo and Matt McIrvin were visiting me and talking about various ideas for the design of the first CD, Needs More Wanger. At some point Kibo said that he thought it would be great to have a bonus track on the album where someone kept repeating "SECRET BONUS TRACK" in a monotone over the music. I happened to have a digital recorder, so I fired it up and had him talk into it.

While I was sleeping that night, the rhythm of Kibo saying 'BONUS TRACK' seeped into my brane and I found myself thinking of it in the context of a jazzy bass line. When I woke up in the morning I recorded the bass line and then added some other noise using various other instruments I had laying around, and that was pretty much it.