Funny enough,out of the 3 cockatoos I have had, a sulphur crested cockatoo, a moluccan cockatoo, and now an umbrella cockatoo, I found my sulphur crested cockatoo to be the loudest screamer (morning alarm clock) and before bed, but that is normal, and didn't last long.
My moluccan was the quietest and just went with the flow. He hardly ever screamed.