There is also little reason to use "Quiet Steel" for exterior panels, since the desired effect, i.e., absence of vibration, can pretty effectively be done with either stick-on visco-elastic damping sheet, or spray-on materials.
BTW, I have used "Quiet aluminum" from MSC for floor sheet in a Class 8 truck cab, on a prototype basis, and found only a very small reduction in sound transmission through the floor, due to the lack of a coincidence peak in the material. It didn't jsutify the increased expense and somewhat greater difficulty in fabrication.
Regards,
- R