I am usually quiet at home around family as well, but that is mainly because my parents are from a different generaton and its always a really tense vibe in the house ...
so i think it depends on what your family is like in terms of how you get along with them, whether there is a friendship element ..
then again my sister used to talk alot when she lived with us so maybe its just me.
but i dont really relate too well with them and my opinions tend to be shot down alot through prejudice arrogance so i tend to stay quiet.
i know alot of people are loud around their family though which is great and how it should be.