I wonder if the sex of the bird makes the noise difference.
We have a male Sennie. He can be *looooouuuuuuddd.* Maybe not as loud as a Cockatoo, but definitely up there for a creature as small as he is! Like Michael said, the alert scream they let out can be ear-piercingly shrill. (And we wondered why his prior owners -- he's up to at least his 4th home with us -- were banging on his cage bars when he screamed!) Anyway, I noticed that it's not as though he's loud for no reason. He's primarily driven by food and boredom. He would be sitting on our shoulders 24-7 if he could. He seldom makes a noise when he's on either of us. He also tends to be more vocal when strangers (to him) are visiting us (his way of alerting the flock to intruders I think). And he knows what the kitchen is for. Whenever either I or my fiance gets into the kitchen to start making food, watch out! It can be quite unbearable. And it's not as though we reinforce this by giving him food until he shuts up. We know better! I've thought about moving his cage so he can't see the kitchen. But we're in a tiny apartment, so we don't have much leeway with where he can go. Plus it's nice to have him in the dining area so he can see us when we're in the living room/dining room just hanging out.
Anyway, these are just my experiences! On the plus side, even though his screams can get annoying, he can be quite talented at talking. He will randomly say "I love you," say his own name, and laugh at many jokes along with us. He's also excellent at imitating home noises like the microwave, creaking doors and the telephone. So it all has its pluses.
