Well I work with a mechanic here and he heard your sound clip and said that it is probably knock.He did also say that you could have carbon build up and that yes the water trick down the throttle body will work or intake cleaner just remember if you do either change your plugs after because they will be full of crap

REDLINING IT ALL THE TIME 1998 mtx zetec contour 17.1 @79mph open element air filter ford 9mm racing wires dtm style exhaust