A student assignment: “This particular piece is a field recording that was recorded by James Koetting in 1975. The music was created by the postal workers canceling stamps in the University of Ghana post office in Ghana. The whistled part is from the hymn Bompata, by the Ghanaian composer W.J. Akyeampong (b. 1900).” And J. Koetting?
This is what you are hearing: the two men seated at the table slap a letter rhythmically several times to bring it from the file to the position on the table where it is to be canceled (this act makes a light-sounding thud). The marker is inked one or more times (the lowest, most resonant sound yuo hear) and then stamped on the letter (the high-pitched mechanized sound you hear)…. The rhythm produced is not a simple one-two-three (bring forward the letter — ink the marker — stamp the letter). Rather, musical sensitivities take over. Several slaps on the letter to bring it down, repeated thuds of marker in the ink pad and multiple cancellations are done for rhythmic interest….
The other sounds you hear have nothing to do with the work itself. A third man has a pair of scissors that he clicks — not cutting anything, but adding to the rhythm…. The fourth worker simply whistles along. He and any of the other three workers who care to join him whistle popular tunes or church music that fits the rhythm.