This engine is meant for Skylon spaceplane, an unmanned cargo vehicle. As for noise, there are no reasons to have it overflight any populated areas. I presume there would be less noise abatement technologies employed due to need for efficiency.
As for emissions, close to none. The engines are supposed to burn hydrogen, and other emissions (brake pads wear, in-orbit maneuvering via cold thrusters) are minuscule.
As for emissions, close to none. The engines are supposed to burn hydrogen, and other emissions (brake pads wear, in-orbit maneuvering via cold thrusters) are minuscule.