In my personal opinion and experience, toos need A LOT of attention and constant entertainment. Now, this 'constant entertainment' doesn't necessarily have to be a person playing with them, it could be other birds. I have two lesser sulfur cockatoos but poor Linus has only been here a few months and he has deep wounds in his soul, I think, so I won't use him as an example. Freddy, on the other hand, has been here for a couple of years now and is now very much settled in his new home and routine so I will tell you about him.
He was 21 years old when he came to me, his owners had severe medical issues which made them lose their business and home so they had to move in with her brother who would not take Freddy because he was a screamer - BIG TIME! He also plucked his legs but that is neither here nor there. Freddy loved his owners but he only saw them at night, when they came home from work so he wasn't been kept at a strict solar schedule and, on the advice of his avian vet, he was been fed Harrison's High Potency (very high in protein) so the poor thing was not only overly hormonal, he was alone all day long. Result: constant and very loud screaming.
It took ten months for him to stop and, it might sound like a long time but considering that he had lived that way for 21 years, I don't think that it was that very long. It did seem long though

because, as you have figured out, these birds are LOUD LOUD LOUD! I put his cage in my livingroom and, as I stay home, he pretty much spent many hours either on me or with me nearby. I answered every single scream, sometimes I would just walk up to his cage and talk to him for a while, sometimes I would take him out and allowed him to be on me. I kept him (as I keep all my birds) to a strict solar schedule with full exposure to dawn and dusk and immediately stopped feeding him the pellets, switching him to gloop and raw produce for breakfast and a seed/nut mix for dinner. As the months went by, he screamed less and less and I started bringing him into the birdroom with me. He had never seen other birds and it took a while for him to dare venture out on his own but, slowly and surely, he did until he moved in there. He still screamed a bit after that, especially when he heard voices outside the door (my husband always forgets to whisper in the evenings) but he eventually stopped. He lives cage-free in a room with other birds which also live cage-free, he gets pieces of wood to chew on and, most importantly, his beloved hard cardboard boxes in which he spends hours scratching and chewing the inside. He has his little routines that he, apparently, needs to feel good and which I accommodate (the jumping on my shoulders when I come in so we can have our 'love session', the 'papapapa' where he stands at my eye level and staring into my eyes, clicks his beak while I click my teeth in rhythm, my feeding him his 'salad' (the daily leafy greens - he is a GREAT eater) before any other birds gets anything, my swinging him from a towel while I go WEEEEEEEE... little things but important to him. He still makes his loud calls but they are short-lived and they mostly happen in the morning and evening, which is normal. Nowadays, when he hears our voices outside the door to the birdroom in the evenings, he says "ByeBye" a couple of times in a sweet soft voice and shuts up.
Now, I know that most people out there would tell you to ignore him when he screams and only go to him when he shuts up (they call it rewarding 'bad' behavior when you do) but I don't agree. The way I look at it, they don't scream because they are been 'bad', they scream because they NEED company, just like a baby would cry when left alone... out of fear, insecurity, loneliness. And I would never not answer a baby's cry. I think that, once they see that they do have company all the time, they stop screaming. It doesn't happen overnight but, in my personal experience, it happens if you are persistent and consistent - of course, this implies that you are there all the time, too! It's a lot of work, I won't deny that! But, aside from the ear splitting inconvenience of their screams, the fact that I think that they do it out of anxiety, loneliness, fear of been alone kind of breaks my heart so I really can't see myself just ignoring them.