The 370z is bound to rattle, it's not a high end luxury sports car-
If you have a used car, then maybe the original owner put new speakers in and dropped a screw or something similar.. If its really bothering you, take off the door panel, get some sound deadener and fix it yourself on the weekend
My back hatch rattles from those plastic panels on the trunk hatch. I even have some sound deadening material..
Get a loud sound system or a louder exhaust