while writing music, i took a break.  i heard a plane fly overhead..  well, not quite overhead, but probably a few miles away, and as the low frequency hum that it emitted descended in pitch, as it approached certain frequencies of the chromatic scale, it grew louder, then faded out until it approached the next frequency (so it faded in and out about every three seconds).  so i thought i was hearing music.  i don't know if this was my mind adjusting noise to music (in that case, it'd be due to my culture) or if it was that the ear naturally resonates at certain frequencies (and maybe that's why the western scale uses the freqency intervals that it does).  hm.