The flush toilets at home are noisy.* So ... why shouldn't marine toilets be noisy too?
Different noise.* Home toilets work by gravity and siphoning.* The most noise comes from breaking the siphon.* That is the part that is hard to quiet down.* Marine toilets have a prolonged pump and grind noise that resonates through the structural members of the boat.* Spaces are small and hard to isolate noise wise.* It makes it a very difficult problem to solve.* Even though some are advertised as quiet flush, they are not quiet.* The Vacuflush is the quietest head that I have had, but they are no fun to change the duckbill valves.*
Maybe we should work on a human system that uses food to 100% efficiency and produces no waste.