Did you ever pull the subwoofer? Mine's not sounding too healthy. I did pull some of it apart to get a better look, but I didn't get all the way in. I tried to remove the screws holding the sub in the box, but it wouldn't come out. I didn't pry too hard, as I didn't want to break it.
It kinda looks like the seatbelt and possibly the seat on that side both need removed for full access.
I got the outer panel pulled away enough to access the screws holding the sub into the box, but not enough to pull the whole box. Looks like that requires pulling out a lot more trim and at least the seat on that side.