Yes the case will have an a acoustic sounds and ring in a special tone when dropped on the concrete floor. To drown out your cursing when you drop It.lol
But seriously the best way I could put it is just because you can't see electricity following through a wire, doesn't mean it's not there.
Maybe the circuit board,(which of coarse needs to be isolated from any shielding that's a conducting metal, what ever the metal is). Creates a radiated invisible field that you can not see, and of coarse this field will be affected by different metals in its close proximity, and in affect change the way the end transducers (iem's/headphones) sound.
Just like different metals in music instruments like a trumpet, change and alter sound,(just maybe). I wouldn't rule these things out. Electronics is very complex.