This actually could be several things. My first thought would be a possible wing injury. Especially in younger birds if they have had a wing injury they will flap that wing and squack, scream etc. Other times they may use this same behavior for attention getting and begging. Usually their "begging" is done with both wings extended slightly from the body with more of soft quiet chirp while and injury will usually result in much louder screams. If you bird hasn't already been since it is so young it does need a complete vet checkup which will also let you know if the wing is something that needs to be worried about or just a greeting behavior.