Schizophrenia, Undifferentiated Type: This diagnosis is considered because the patient presents with persistent auditory hallucinations without other psychotic features, which is a hallmark symptom of schizophrenia. However, the lack of response to antipsychotics and the presence of external hallucinations by both ears may suggest other underlying conditions.

Psychotic Disorder Not Otherwise Specified (NOS): Given the patient's symptoms do not fully meet the criteria for schizophrenia due to the absence of other psychotic features and the nature of the hallucinations, this diagnosis could be considered.
Major Depressive Disorder with Psychotic Features: Although the patient does not exhibit delusions or disorganized thoughts/speech, depressive episodes can sometimes present with isolated psychotic symptoms, including auditory hallucinations.
Bipolar Disorder with Psychotic Features: Similar to major depressive disorder, bipolar disorder can present with psychotic symptoms during manic or depressive episodes, though typically, there would be other mood symptoms.

Temporal Lobe Epilepsy: This condition can cause auditory hallucinations and should be considered, especially if the hallucinations are complex or if there are other neurological symptoms. Missing this diagnosis could lead to untreated seizures.
Brain Tumor or Cerebrovascular Disease: Any mass lesion or vascular disease affecting the temporal lobe or other areas involved in auditory processing could potentially cause hallucinations. Imaging studies are crucial to rule out these conditions.
Neurosyphilis: A classic cause of psychiatric and neurological symptoms, including hallucinations, which can be missed if not specifically tested for.

Charles Bonnet Syndrome: Typically occurs in visually impaired individuals but can rarely present with auditory hallucinations in the context of significant hearing loss. The patient's complaint of external voices by both ears might suggest a consideration of this, especially if there's underlying hearing impairment.
Musical Ear Syndrome: A condition where individuals, often with hearing loss, experience musical hallucinations. While not exactly matching the patient's presentation, it's a rare condition to consider in the differential for auditory hallucinations.
Peduncular Hallucinosis: A rare condition caused by lesions in the peduncular region of the brainstem, leading to complex hallucinations, including auditory ones. This would be an extremely rare cause but should be considered if other diagnoses are ruled out and there are suggestive neurological findings.