Ok, while I was letting my drone update firmware, I heard a whistling noise. I was in another room. It sounded like an "all clear" signal (who-HEE-whoooo). I thought maybe it was telling me it was finished. But it wasn't. It finished update, and I did the RC with no problems. Then, in the middle of the night, the same whistle woke me up. Nothing was charging or plugged in. Went back to sleep and haven't heard it again. Was this drone-related, or am I hearing things?