Vacuum passes neither heat nor sound.
On the other hand you can not find it in convenient easy to install panels unless you work for NASA or some other organization that doesn't have to count (pinch) pennies.
Until then us common folk are best off with one of few solutions, add mass (lead) to absorb the sound or add vibration dampening to lessen the noise and of course to add baffling - i.e. foam or sound reflective surfaces (the paint on stuff, and perhaps carpet).
If you "really" want to insulate for sound - get a roll of sheet lead and apply your own lead sheet (use a PSA) to your existing walls - after all lead is soft and bendable and cuts easy.
Lead Sheet from Rotometals
Don't make your engine compartment so well 'sound' sealed that it starves for air.
Of course racer's hate mass, but how many of them care how loud the engine is?