My rattles when it is freezing outside but goes away when it warms up. But like one reply said put dampening between the speaker and bracket. Also those base speakers (not subs on the door) may not be able to handle loud bass, so it could be the speakers.
2011 Mustang Convertible Kona Blue - FRPP Sport Axleback - Bama 93R - Blackout Panel - Tri-Bar Valve Caps - Airaid CAI - 4x JL Audio C2-570x - Alpine MRP-F300 Amp - Speaker Sound Dampening - 27% tint all around.
In the future: Kona Mirror Covers, Boss 302 Suede Steering Wheel, Possible Mono amp/Sub.