Buzzing, Clicking, Vibrations in the Hypnagogic State

I know I can attest that when you are nearing what is called the 'Hypnagogic state' - the state of being between asleep and awake - you can start to feel odd vibrations and sound within your head. From all of the literature I have read on the subject of Astral Projection almost all sources state that this state is the crucial moment to leave the body. Many times this is preceded by sounds in the head - a kind of buzzing sensation that feels oddly like someone is stretching a rubber band from your head and plucking it with a sudden feeling of falling back on your pillow. There are other cases where people hear a sound like chimes or bells just at the moment of unconsciousness. Others hear things like 'horrendous gushing sounds', 'weird ringing/buzzing noises', 'rushing to roaring up to sounds in the upper frequency scale like whistling', and 'very low hum, like a fog horn'.