Your question seemed rhetorical, that's why nobody answered... If I had to guess I would say no, it is not possible for them to do it any quieter. The man has horse legs.
1) They probably could, but it wouldn't be as pleasurable for either of them and it would be more like teasing rather than actual sex. 2) Talk to your roomie and tell them how it bothers you and if it stops, it stops, but you can't *really* expect them to change how they're having sex just to suit you. At least they're not doing it out in the open. If it really becomes an issue for you, then it's time to go your seperate ways.
Anatomy Snausage Time: I'm able to cum and keep it as quiet as a church mouse. Other male buddies with their female mates seem to be able to do the same when they're in another room as well. Women, on the other hand - not so much. Or the ones that are able to keep it quiet seem to be able for a while until one of those super-waves of pleasure hit their pussy and then all caution seems to be thrown to the wind. I'm guessing the difference is the amount of nerve endings between genders. Supposedly women have a lot more than men, so maybe it would be uncontrollable for women to keep quiet the whole time. Again, I'm only guessing the reason because from personal experience. Another person's experience may be a complete reversal to mine.