The BAs do vibrate (some more some less) and it's recommended that you glue them to the shell. Otherwise they will rattle, if not from its own vibration then from you moving around.
Filling shell with silicone will change the sound of the BA to a warmer tone and dramatically improve THD (in my measurements typically 4x reduction), but then you can't really use vented drivers such as 3800 etc.
I used to like filling them solid but then they became impossible to repair if anything broke sadly :\