PDD NOS Hearing voices

My 8 year old boy was diagnosed  with   PDD NOS/Anxiety and is very high functioning except that he suffers from anxiety. He has said for a year and a half that he is tormented by the noise,chatter, laughing in his head. He says he hears constant chatter and laughing all the time.  He says that the voices will   talk about him and he fights them all day long.  He is very present to reality, is doing well academically, learned to ride a bike wants to have friends. His complaint is very consistent.  He struggles to make peer friendships and this seems to be when the noise is the loudest but he continues to want to have play dates even though it is very stressful him. Here really hates loud places with lots of stimulation. He is taking Risperdal and Norotin- we just discontinued the Zoloft. The meds are not working. He is exhausted by the constant battle to have the noise go away.  Has anyone else experienced this and could there be an organic reason for the noise.  Is the anxiety giving him the noise in his head or is the noise causing the anxiety? If you have any ideas please respond.Thank you.
ideas please respond.. Thank you.