Hello johnmel22, and welcome to the community!
Metal plating could generate interference with the signals recorded by the Shake, so we recommend using something different, such as a thick sheet of acrylic (plexiglass) that should suit your needs of transportation without having the negative effects of the other material.
Metal can sometimes act as an “antenna” of sorts, picking up RF interference that can be a bother for some components, as you have already noticed. Another solution would be for you 3D printing a suitable case (an example here: 3d printed case) that you can use to move the Shake around.