"Creates a sound as loud as a car door closing" -> I assume this means at ground level? I can't imagine even the propulsion being that quiet let alone the sonic boom.
Interestingly, it’s not just the volume but also the pattern of the boom that can be altered by changing the design of the plane. There’s a great discussion of this here: https://www.elidourado.com/p/50-years-supersonic-ban (Scroll down to the images of the sound wave)