Look guys I only got a 3rd but this is really not that subtle.
Sound is simply a disturbance on the fluid medium in which the disturbance is generated. No medium; no sound.
Look at it this way. You descend over the Pacific gently. Everything is fine until you get to 0 amsl. Then the wings fall off.
Why?
Why didn't they fall off before?
Now reverse the argument. You create a sound in the dense medium known as air but as you climb to 3000000000 feet. No sound.
Actually of course Space is not a vacuum so there will be sound. It's just that it is so minimal you don't notice.
What about the engines vibrating? Well they will propagate sound through the vessel but it won't leave the vessel because the vibrations have no surrounding medium to vibrate. Does this mean anything? No. The damping effect of the air on the airframe is negligible by comparison.