I too have a rattle around that area, one weekend i took the fascia and dash all the way out. Checked the parts i had pulled out, no loose bits, stuck my hand into every nook and cranny under the dashboard, again no loose bits.
So went for a drive with all the stuff out. The rattle was still there but sounded more like metal on metal, stuck my head outside the window while drivin and it sounded like it was comin from under the hood, checked under there but no loose bits either. Pulled the grill off (where the water runs down into off the windscreen) no loose wiper motors or bars or anythin).
So im guessing its inside the car, right up under the dash, something banging on the chassis for it to be audible outside the car.
Im positive thats where the noise is, but cant get to it with taking the whole dashboard off, which is a big project. So if anyone has any ideas what it could be lemme know before i got writing off my car
cheers :-)