All of Number Twelve, Grimmauld Place seems designed to remind Sirius of the dark years of his childhood, with its gloomy, pest-ridden rooms and the Black family tree with his name burned off. But the one object that really drives home exactly how much of an outsider Sirius is to his own family is the portrait of his mother that hangs in the entrance hall of Number Twelve.
Every time someone makes too much noise or disturbs the portrait in any way, the painted Mrs. Black will start shrieking catchphrases the real Mrs. Black enjoyed: nonsense about blood traitors and filth that clearly gets to Sirius. Mrs. Black's portrait is not a fully realized character, since her responses seem automatic and not complex. Instead, her constant shrieking if anyone in the house speaks too loud underlines how trapped Sirius is at Number Twelve. If he moves a muscle out of turn, the house itself starts to yell abuse at him. No wonder he goes stir crazy over the course of a year imprisoned there.