A two-parter indeed! That one really takes a turn at the end, eh? First, shushing. I feel like there is no way to be shushed without feeling insulted, or at least having the wind taken out of your sails. And certainly, for a person who enjoys making a little noise, screwing in stony silence feels unsexy. At the same time, I completely understand not wanting to have to hear your roommates fucking, or not wanting your roommates to hear you fucking.
It's like, we all know what's going on in there. Duh. And obviously nobody should feel ashamed about sex. And also thin walls are thin walls, what can you do? Then again, depending on your relationship with your roommates, ugh. I say maybe just turn on some music or something: that says hey, I'm trying to be cool about this, which is nice.
And the second part. Ok. It is awesome that you are willing to experiment for your guy. But yeah, seriously, I get that roughness in general can kind of be negotiated on a case-by-case basis as it happens by using body language and stuff, but choking definitely is in the territory of let's set up some boundaries beforehand and possibly a safe word/gesture.
Especially if we're talking about the kind where you pass out a little bit to prolong the orgasm or whatever (but I would think then he would want you to choke him?) because there are wrong ways to do it that could injure you. Or if he's more into simulated violence/rape, then it is definitely going to be a good idea for you guys to figure out what you're comfortable with beforehand, so that you don't come away feeling violated.
How to bring it up? You seem like you're doing a good job trying. I don't know if he's embarrassed or what, but I would just say it point blank in a non-judgmental just trying to get things figured out sort of way. And if you're wrong, whatever! It shouldn't be a big deal.