Hearing voices, or auditory hallucinations, is a symptom I'm not
sure if I can say common, in psychotic disorders such as
schizophrenia, the one we're most familiar with, and bipolar
disorder and extreme depression. I'm not an expert, just someone
who has read up a little, so feel free to correct me if I'm wrong.
Or, some people with neurological illnesses may have it. Oh so it's
actually not mental all the time.
Anyhow, we're not psychiatrists or psychologists so let's not cause
mase101 undue worry. 
