i don't even know about the rattling, haven't invested in a big enough system yet.
but my plate has 4 screws to begin with (95-97 style trunk), and it seemed to hold the plate real well. i ended up replacing them with lights, and drilled out the metal below the bottom holes so i could have clearance for the wires. so 2 more screws/bolts would probly help you out a lot.
