gary- i believe you are thinking of the 'tap,tap' simply in the description of the scene.. she is 'tapping' the glass. i assure you, it isnt supposed to sound like a 'tap'. it is supposed to be a BOOM, or DUB as you call it. even with my mid-grade vega, it shakes the house.
i think you may be confusing your expectations with whats actually on the soundtrack.