Andrew. the rattle might be the center defogger duct as there was a TSB on how to fix it. Here are the instructions on how to fix it. I also emailed you with the pictures on how to do this fix.
Robbie
Interior - Rattles From Instrument Panel Area
NUMBER: 23-027-03
GROUP: Body
DATE: November 28, 2003
SUBJECT:
Instrument Panel Rattle Sound
OVERVIEW:
This bulletin involves modifying the IP center defroster duct.
MODELS:
2003 - 2004 (ZB) Viper
NOTE :This bulletin applies to vehicles built prior to November 1, 2003 (MDH 1101XX).
SYMPTOM/CONDITION:
Rattle sound from IP defroster grille area may be heard when driving over rough road surfaces. The defroster duct flange is touching bottom of defrost grille and/or IP substrate.
DIAGNOSIS:
If the vehicle operator describes the Symptom, tapping on the IP near the defroster duct will cause the rattle sound and confirm the condition if present.
REPAIR PROCEDURE:
1. Remove the defroster grille from IP (using trim stick or equivalent).
2. Remove the defroster duct mounting screws (2) and defroster duct (Fig. 1).
3. Using snips/cutters, remove upstanding flange around entire outlet side of duct (Fig. 1).
4. Remove any loose debris from the defroster duct area.
5. Reinstall duct with two screws, tighten the screws to 1.6 - 2.2 Nm (14 - 20 in. lbs.).
6. Reinstall defroster grille making sure it is secure around entire outside edge.
