The vibrating is essentially your body going into sleep paralysis. that means your body is asleep, but your mind is still awake. you need to be in sleep paralysis in order to lucid dream, and astral projection is comparable to a form of lucid dreaming. you are basically putting an image of yourself laying in bed (or whatever youre going to look at) in your mind, and eventually it manifests itself as a dream and it feels as if you are having an OBE.
dont fight the vibrating feeling at all. in fact, try not to pay attention to it because when you do (at least for me), you start to get excited which wakes your body up and you snap out of paralysis. just keep at it and youll have an obe/ld eventually, gl.