This happens a LOT It appears to be a form of Auditory Paredolia where the brain takes random sounds and tries to make "words" out of them.------It sounds just like a lot of people whispering, but you just can't quite make out what they are saying.
---In MY experience it seemed to be caused by a slow running electric fan, either a box fan or an AC system set on low.
Do not confuse this effect with the deliberate random noise used in so called---"Ghost Boxes". It has a different sound. Here the paredolia sound like an ocasionall actual word like "yes" or "No" or someone's name--as in "Mike" of course we also have auto suggestion playing a part here as well as paredolia.-----HOWEVER we do sometimes get some "messages". There is no proof of "spirits" and even a real message is not evidence for them--truth is, we do not KNOW where these messages come from YET. What is a real "message" vs mere Paredolia?
Use the "Five syllable rule" Ignore ANYTHING less than five syllables/words in length. One word or syllable, generated randomly, might sound like a real word by chance alone. two or three in sequence pushes the bounds of probability---But FIVE or more makes random possibility very far into the Zero range.------But as I said, their origins are UNKNOWN, do not make "paranormal assumptions".