When I was a child our school took us to the Physics Exhibition. I saw a bell in a case was ringing. The supervisor made inside the case vaccum and the noise cut off.

Now I am studying mechanical Engineering, I have this question why manufacturers don't do something like that. I know it will make some problems. For instance, the heat transfer will be more challenge. But aren't they solvable?

They can put nosie damper after outlets and before inlets.

I'm sorry about my English.