I searched this site for lost voice because I knew that Dr. B had answered this question before. Below is our Avian Vet's answer to a bird losing his voice or having a voice change....
This could be a serious problem. One of the only things I am aware of that causes voice change is Aspergillus infection in the trachea. Birds do not become hoarse from screaming, they have no vocal chords like mammals. He should be seen by an avian specialist as soon as possible.
