Sirius Black has never been known as a quiet person. However, he wasn't abnormally loud either.
He was remembered as a boy whose laugh bounced around the room, whose voice carried whenever he spoke, and whose footsteps echoed down the hallway whenever he walked. It was believed he did that on purpose.
He did.
Sirius Black had a sound to him. One that buzzed under his skin and mingled with his magic, creating a sort of...energy around him. One that people were naturally attuned to. He operated on a frequency that made others hyper-aware of him.
So when this boy was quiet, it was a cause for concern because when Sirius Black went silent, the energy disappeared. The silence that permeated wherever he was became oppressive.
In those moments, anyone who was around him was left unnerved by his lack of sound. Not even his magic reacted, choosing at that moment to become eerily calm.
He always spoke in a deceptively soft voice afterward, and unlike any other time, those around had to strain to hear his words.
Everyone had a different reaction to his silence, but only one truly mattered.
Remus hated the silence. He always found an excuse to leave. He never wanted to believe his friend was a monster, but in those moments, rare as they were, he could not see a difference between his wolf on a full moon and a silent Sirius Black. It unnerved his wolf; it made him believe his friend to be a predator. Something to be eliminated.
Peter hated confrontation of any kind and yet reveled in the drama and excitement. He was torn between anticipation and fear. He latched onto Sirius because Peter always seemed to know who was powerful. He smelled it and sought it out like a rat to cheese, and Sirius Black was powerful. He believed that the silence was greater than the sound; he believed he truly understood where Sirius's power was, and he eagerly waited until he could get the tiniest bit of taste.
When Sirius Black's sound returned, a collective sigh of relief was released. However, the moment it did, people felt a tingle on their skin, their hair stood on end, and shivers went down their spines. It felt as if they were in a horror movie, and yet...it was wrong. The danger had passed. The sound was back; their hyperawareness was back, along with that slight buzz in the air. Everything should have been back to normal, and yet...it took days until that sense of normalcy returned.
James, however, knew Sirius like the back of his hand and believed Sirius to be his twin flame. In those moments of utter quiet, he would simply stand behind his friend, an impassive expression plastered on his face. He knew what was to come—the evisceration and annihilation of whoever earned Sirius's silence. Briefly, very, very briefly, he felt a sliver of pity before he squashed it. Whoever caused his friend to revert had it coming.
Because you see, Sirius Black was born silent. When he was still in the womb, he hardly moved or kicked. If not for his heartbeat, everyone would have thought he died in the womb. While other babies screamed and cried the moment they could, Sirius did not. He made a sound when he wanted to be acknowledged, when he was hungry, or when he needed to be changed. He simply saw no reason to make a sound otherwise until he learned how to utilize it.
James Potter, unlike everyone else at Hogwarts, knew the truth.
It was his sound that was dangerous, not the lack of it.