Why are some free hubs silent and some are noisy?

[keith davies]

Why do some wheels have a silent freehub - my old ones - and some have a noisy freehub - my new DT Swiss? Just curious

 

[JayKosta]

Probably differences in the way the mechanical 'lock-up' works - ratchets, cams, etc. And the type of internal lube. Also, how the internal vibrations (noise) gets propagated outside as sound.