Flanging is a time-based audio effect that occurs when two identical signals are mixed together, but with one signal time-delayed by a small and gradually changing amount, usually smaller than 20 ms (milliseconds). This produces a swept 'comb filter' effect: peaks and notches are produced in the resultant frequency spectrum, related to each other in a linear harmonic series. Varying the time delay causes these to sweep up and down the frequency spectrum. more info go here http://en.wikipedia.org/wiki/Flanging#Origin to hear some of it fo here http://tools.wikimedia.de/~gmaxwell/jorbis/JOrbisPlayer.php?path=Itchycoo+park.ogg&wiki=en very cool shit when ur high
i used to do that as a kid. i would hum and find the pitch of my dad's engine, just because it sounded so cool.