I have a painter's mannequin/doll/figure in the direct line of the air vent. I'm not saying the sound WASN'T hypnagogia. It's just that something happened in the physical realm that could out rule it.
Also ... I think, a few days ago, I was astral projecting right before I woke up from sleep. I had forgotten to take off my necklace with an amethyst stone on it before I went to bed. I don't remember much of my "dream" but what I do remember is being over the earth as a ball of light and a light source in the distance. The light source was like a black hole except blinding white light. I wondered what it'd be like to travel to and through the light. But, as I thought that the crystal started to vibrate, pulse, and hum. Sending me back to the waking world.
Also ... I think, a few days ago, I was astral projecting right before I woke up from sleep. I had forgotten to take off my necklace with an amethyst stone on it before I went to bed. I don't remember much of my "dream" but what I do remember is being over the earth as a ball of light and a light source in the distance. The light source was like a black hole except blinding white light. I wondered what it'd be like to travel to and through the light. But, as I thought that the crystal started to vibrate, pulse, and hum. Sending me back to the waking world.