if you pull the carped away from either side of the rear of your trunk, you will notice a vent. it has a plastic grating and a plastic gutter to keep water from leaking into your trunk. behind the grating (looking from the inside) there is a rubber flap that covers the hole. when air pressure is increased or decreased in the car, these flaps open. when a large sub is moving the air in your trunk the pressure causes these rubber pieses to flap loudly in a fart like manner. put your head next to each side of the trunk whil playing oyur subs and you will hear it. i used needle nose plyers to rip the top part of the flap out, but left the bottom and the watter gutter in. no more fart.
