ive heard that time out as suggested by skyes mom can be a useful method. if already in the cage, then covering it over for 10 mins or so.
its a hard behaviour to manage seeing as youre not around when your noisy baby is screaming. have you done much in the way of foraging? there is currently a topic calling 'foraging'. its an essential bird behaviour and activity - by removing it from their daily activities by giving them a constant source of easily accessible foods, it can lead to an increase in other behaviours, such as screaming and feather pulling (in the more extreme). what would normally take several hours in their day is reduced to minutes. im reiterating something i read, but it was put in a way that made you think "huh, thats makes alot of sense".
maybe if hes got something else to do, and is distracted with that task, he will be less inclined toward attention-seeking behaviour.
also, if the house and area is very quiet when youre not around, this can stress them out and make them more noisy, apparantly. in the wild, silence suggests a predator nearby. and no matter how friendly and tame our bundles of love are, they are still only a few generations removed from wild birds. you could download some ambient nature albums, like rainforest sounds etc to play when youre out. i got a series aptly called 'sounds of nature' which has atleast a days worth of audio across several ecosystems

my girlfriend like to give me grief about it, but if it works, it works. its also an opportunity, with some very basic audio recording software, to record and loop a ten minute or so phrase with your voice that you can play when youre not around to help train with speaking.
anyway, thats about my knowledge exhausted. some food for thought...