I had never heard of the word ACOUASM until Little Rabbit mentioned it. It kind of a neat word. It can be like a dream or a it could even be a figment of your imagination. Just what is an acouasm?
Acouasm: a nonverbal auditory hallucination, as a ringing or hissing.
Acouasm originates from the Greek word ákou which means "something heard". And ákou is a stem of the word akoúein which means to hear.