All These Little Metal Things at first conception. I had been walking down the street trying to think of things to write songs about, and saw a manhole and a utility cover and a transformer enclosure et voila.
I've never studied percussion, so notation with a-tonal 'x' heads struck me as exotic for a long time. I use it now mostly as a visual cue when I don't have any firm melodic or harmonic ideas attached to something I want to get down rhythmically. In this case, I never really intended to write a melody for these phrases, but I'll sometimes chart out a vocal line that I plan to add proper melody to later in this same style.