Unusually Obnoxious Dash Rattle

Seems like I've got every squeak and rattle imaginable inside my '16 GT, and adding a throaty exhaust (Outlaws + x pipe) certainly didn't help. This one is the most troubling though, looking for some advice or at least a sympathetic ear.

This particular rattle is somewhere in the dash, behind the silver trim piece on my non-PP car. It's nearly constant while driving, but much worse in a low RPM range of about 1800-2000. My ears tell me it's coming from directly above the glove box, but also maybe from the center vents. If I press firmly on the trim, the rattle mostly stops.

My first step was to pop the silver trim off and cover it with felt tape; made no difference. I stuffed foam insulation in every crevice of the dash and the trim panel, also no good. I then discovered that it was still rattling with the trim removed completely. :headbonk:

Any thoughts? My local dealers haven't been much help (one replaced the clips on the trim panel, no change, and the other basically said "deal with it").

Two possible factors to contemplate:

1) there is a piece of something -- likely wiring or ductwork -- that is not securely fastened (or not fastened at all) to whatever its supposed to be fastened to

2) there is a stray clip or screw sitting against a hard surface

In factor #2, I'm talking about a clip or a screw that used to be affixed to or driven through "something"...and was one of several that - together - secured the "something". But during original installation or subsequent repair, the clip/screw fell or broke or was torn off or was dropped accidentally.

My $'s on factor #2.

I don’t Have the same noise as you but mine is coming from the same panel. The metal that surrounds the heat vents on my base GT sounds like an amplified bowl of Rice Krispies. I haven’t taken it apart for fear of making it worse but I found if I don’t have heat coming through those vents it cuts the noises a lot. It’s all heat related it seems, plastic expanding and contracting.
This is the worse new car (noise wise) that I’ve ever owned. How long have they been building Mustangs, oh yeah, since 1964. Think they would have learned something by now.