Parrots vocalize for a reason.

[my-africangrey-echo]

Parrots vocalize for a reason. They sound off to call a mate with a contact call. They send alarm calls of impending danger. They call their mates to food sources. Do they care about other species within a multi-species flock? Probably not, since their own species is what they are genetically programmed to preserve. Therefore, they must be loud to be heard. Plus, finding your mate in a large flock of several different and brightly colored species is no mean feat. We, as the human caregivers, should realize that vocalization is a critical factor with certain species and treat it with due respect. Is that Conure really screaming, or is he raising his voice in a natural manner to bring you over to him and away from the strange human with whom you were having a discussion?
African Greys, on the other hand, have no need to be heard above other species. They all speak the same flock dialect. For that reason, Greys often are considered quieter parrots than some of those species from multi-species flocks.