No one actually explained why some are quite and some are noisy. Having not taken any of the "high end" freewheels apart, I have always assumed that the noisy ones are because their pawl springs are stronger and/or they have more pawls or deeper engagement teeth.

What's the real answer? I'm curious as well.

And to the guy that made the "noise = energy = bad" comment. Right concept, wrong application. Nice try, though. Save it for the next time you hear some one slapping their feet when they run and use.