I'm not an expert on DID either but wanted to offer you support and offer my own perspective... which may or may not be right for you. Have you ever tried to engage with the good voice? have a conversation and ask why it's there? I'm not familiar with autism and hearing voices but I know some people who believe in spirit guides (very much the same as guardian angels) and engage in conversation with them. I'm not suggesting it is but even if the voice is from within you, you can have a conversation with it.