Rocket launches are LOUD, even to nearby observers on the ground. However, once in space, the vacuum does not transmit sound, so any sound produced by the engines will be contained to the spacecraft.
Are there documented reports of crew members hearing the engines sounding louder, as the rocket moves from the atmosphere to space? Obviously, to be comparable, the rocket should be using the same stage, number of engines, and throttle level.
Related:
However, once in space, the vacuum does not transmit sound, so any sound produced by the engines will be contained to the spacecraft.
No.
The sound produced by the engines is mostly in shockwaves in the exhaust plume, and those leave the spacecraft just fine in a vacuum.
There might be a slight increase because vibrations transmitted through the thrust frame into the rest of the rocket are damped less because the structure is no longer surrounded by air, but air damping isn't very effective so that isn't a big effect.
There will be a noticeable reduction after liftoff, when the amount of acoustic energy reflected by the launch pad gradually reduces to 0.
