You're right, it absolutely has to do with inhibitions. As well, I think some people just aren't as vocally inclined as others.
I have always been "noisy", and I've always found it disconcerting when a guy tells me "be quiet!" It's harder for me to enjoy myself when I'm trying to hold the moans in.

I would think a guy would be pleased to know how much pleasure he's giving me! But not all of them like that... go figure.
I've also found it's true that a partner who is more vocal can encourage the other person to be the same. If a guy is asking me 'how do you like it, baby? Do you want it?' etc., of course I have to oblige by letting him know!
