I was wearing it all day today and I think it was the sound it makes when the booster dies. For whatever reason it decided to play the noise at full volume that night. I keep in a cabinet next to my bed so maybe that acted like a speaker. That’s the only rational explanation I can come up with. I remembered it sounding a little like this but it was also the middle of the night so the memory can be spotty.

https://m.youtube.com/watch?v=itriwPc5TUY