For me, the singers start mostly during silence, like Marsha's, but also there are voices when the heat comes on. The voices, like a number of people talking, comes through the heat ducts and tell me stories but its so confusing I can't concentrate on what anyone, assuming there is anyone, is saying. I've never heard the lines you hear in the movies with hallucinations such as "Kill yourself!" or "Shoot the President!" or "Go on American Idol. Really! You're that talented!". Just mumbled stories.
Right now I've got the jazz station from Spotify on and the heat is whooshing around the kitchen but I'm fairly certain it's just me here this afternoon. But then I've got to get up and go stand under a heat duct to get the full effect, and I'm just trying to get this done. Maybe later.
Hallucinations can occur in folks with bipolar disorder when the depression or mania has psychotic features. Taking a look at what some contributors added to Marcia's site made me feel good because I'm always seeing black bugs flying around the house (I mostly thought I needed new glasses, but bugs in Northern Hemisphere winter? Nah.) and I regaled readers some months back about my being watched by the glass angel in our bedroom.