I robbed this:
"There is a 'vibrato' or 'tremolo' twist knob on certain guitar amplifiers; some Fender models come to mind. It specifically produces that unmistakable wooga-wooga sound, originally intended to emulate a skilled stringed instrument player's fingered tremoloing (think concert violinists, cellists, etc.). It's basically an electrically-induced volume oscillation; one can hear the chord being played, bouncing back and forth on the volume scale, but Marr's good enough to mask the changes. Early guitar rock god Bo Diddley used it extensively on his Fifties singles, which have influenced generations of guitarists, including (obviously) Marr. The distinctive drumbeat of the track is also a blatant/loving Diddley nick".