This little voice most likely comes from your superego, according to Freud.
Superego is our moral and ethical compass - it tells us what is right, and what we should or should not do. In the case above, your little voice told you that you need to behave better when it comes to your interactions with your roommate, which stems from the social norms you were taught while you were growing up, which is part of your superego which aims at perfection.
