Fantastic Z

I had a similar rattle and I found the culprit. It was for me a under dash support brace. The two pieces of metal where the weld were wasn't connected all the way and under a certain load, the dash would rattle. I simply used long reach pliers to bend the metal outwards slightly to stop it.
Here are the pics and in the second one you can see the tooling marks from the pliers.
dash rattle 1.jpg

dash rattle 2.jpg

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Rays GramLights 57Fxx BM w/red centers-Michelin Pilot Sport tires-Motordyne CBE-Nismo red calipers-Z1 (SS lines/Slotted rotors)-Motul fluids-Whiteline diff bushings-Redline fluids-JDM fog lamp-GTR start button-Optima Yellow Top-EVO-R B pillars-Custom GPS mount