I would certainly recommend continued interaction with your pediatrician attempting to identify the source of the pain your son seems to be experiencing. It also seems like you have a psychiatrist that you are working with trying to treat the thoughts and sounds your son is reporting. Intrusive thoughts are sometimes observed in individuals with GAD but they are not one of the defining symptoms of autism-spectrum disorders. Intrusive thoughts are commonly treated with both medication and behavioral therapy. The best recommendation that I can give you is to find a therapist with experience working with children like your son and make sure that the psychiatrist prescribing the medication is monitoring its effects and making changes as necessary if the medication is ineffective.