If you don't feel the need to moan, you shouldn't have to force it - that would just be pointless and make the situation awkward for you. That said, if you're not feeling the need to make noise, he's not doing his job properly imo. I mean, not all girls are super vocal but he doesn't want to feel like he's sexing up a corpse. Unless he's into necrophilia, and lets just not open that door.