> I’m looking for a word that describes the hearing of a ghostly voice or music.

Chants have that other world quality though they are not hallucinatory or ghostly - maybe invoke hallucinations or ghosts.

I was wondering what makes a chant a chant?
Is it only the intonation or does it prescribe to certain rules of poetry?
Does it necessarily have certain rhyme scheme and number of basic lines that are then repeated?