I just got an '04 Overland and noticed a prominent lump under the carpet on the floor of the front passenger side seating area. I've not yet pulled up the carpet to find out what it is - thought I'd check here first to see if anyone else has that too.
Possibly a misplaced jack or jackstand. I had to work the floor of a Cherokee over with a rubber mallet a 2x4 and a mini sledge. Trade in came in with a very nice bump in the floorboard. Looked under neath and you could see the imprint of a jackstand. Either slipped off the frame rail or the jack was dropped with the stand in the wrong place.
If the lump is not hard then it could be bunched up padding from a prior carpet removal. Old sock or a bag of drugs hidden by a previous owner.
I believe that is the air vent to the back seat area, it runs under the R/front seat, I had to pull my carpet up it in that area a few times seaching for a windshield leak, so I am fairly sure that is.
These all are possibilities. The only way to tell is to pull up the carpet and check or look underneath for a dent from the bottom. I was thinking bolt or nut, or the rear seat heat duct. Then again it could be a wad of $100 bills
Thanks everyone for the replies and ideas. It turned out to be an electrical box which I believe may go along with the stereo amplifier that was installed. It's just a rectangular box with wires coming out of it. No drugs, no rock or jack damage, no dead mouse, and no money. I ended up moving it closer to the sill so it's not right in the middle of the floor. Since I had an idea it had something to do with the amplifier and I had looked under the car and found no damage, it really wasn't driving me that crazy not knowing for sure.