on my Z I had a rattle that was the Carrier Bearing (sounded more like a knock and was more toward the center of the car and underneath), also on my Z I found a nut that came loose in the top part of my hatch behind the bottom plastic panel. Just something to check ** on my 200SX I had a rattle that came from the front (front Wheel Drive) it ended up being the Half Shafts (would be rear end on Z) Not sure if helped much but maybe it is a place to start