Philip listens

Acts 8:30 - Then Philip ran up to the chariot and heard the man reading Isaiah the prophet. "Do you understand what you are reading?" Philip asked.

I wonder why the eunuch was reading aloud. Most people read silently to themselves unless they're reading to someone. Was the eunuch reading to someone else in his company? Was it just his custom to read aloud all the time? Was he trying to teach someone or to learn from them in turn through his own reading?