Swapped out entire interior in my wife's tan and black 98 GT ragtop with an all black interior, including new dash, from a low mileage Cobra. Hit a bump or pothole and something rattles or clunks in the dash. Sounds like behind the center A/C vent near the firewall. I took the new dash out, checked all wires and cables, put a brace on top of the air door so it doesn't jump up and down, but the dash still made noise. I took out the radio and CD, center bezel, passenger air bag, glove box, and instrument cluster and my wife drove while I checked it out. No luck. Tried it with vent, heat, and air, no difference. Damn if I can find the rattle! Any hints?