We had a sulphur crested cockatiel called Tilly for several years. It had a chirruping squawk that rose in volume and cadence. Then she looked satisfied, and did it again. She never talked, but would chunner to herself with a speech-like rythm. I also had a neighbour who had a talking African Grey called Trooper, mostly because it cursed like one. We went on a holiday and the neighbour volunteered to look after Tilly, saying that "Perhaps Trooper can get her talking". On our return, on having Tilly handed back, we were informed that "That ****ing bird of yours taught my Trooper to do that squawk".
Full size cockatoos have bigger lungs and beaks. I can only imagine what a horde of them trying to out-shout each other sounds like.