since ive upgraded my system ive noticed the familiar "sub fart". i have a 96 se. and i completely eliminated it w out leaving open hole or removing bumper cover. what i did:
from inside the trunk using tin snips or other stron cutters, locate the vent then using the cutters cut the protruding "bowl" shaped part off. this will allow you to remove it and leave the bumper on. then push in the plastic tabs that hold it in place, It should fall out under the car. then use pliers to rip out the rubber flaps. then use some material to cut a rectangle as large as the piece, i had some plexiglass but 1/2 mdf or sticky duck tape might work also. then use some sheet metal screws to attach the piece, i also put a bead of silicone between the cover and the vent piece to waterseal. make sure the cover is attached to the side that will be on the outside of the trunk, because the vent pushes in from outside. let the silicone dry before installing makes things less messy. also if the screws used protruce from the back side of the vent piece use shorter screws or hach them off. also a dremel is a great tool to have for this.
david