I’ve also always thought it may have to do with social conditioning, but possibly on a non-sexual level. My thought is that guys are (generally) conditioned to be more quiet about intimate things, or things that are good, and more loud in “aggressive” situations. This fits well with the factual observation that men are less likely to talk about personal problems with a friend, and more likely to push the boundaries (be vocal) in an interview. In my head, it’s an extension of the “strong, silent” stereotype, which is often regarded as positive. Women, on the other hand, are (typically) socially conditioned to be more vocal about feelings in general. I wouldn’t be surprised if these conditionings bleed over into how vocal people are during sex.

With that said: I’m a guy, and my gf likes it when I make noises. Once I got used to it, I also learned to enjoy grunting. Grunting is highly recommended.