Those of us who've had the dubious pleasure of owning British bikes from the 60s and 70s will, of course, know what real engine clatter sounds like. I remember riding things that sounded like they had a bolt inside the cylinder, hammering between piston and cylinder head. Others had valve gear that was so loud you could hear it before the exhaust note when your mate was driving up to your house.
Compared with those the NC is almost silent, I guess. But they are a bit noisy for a Honda.