If everything around you was silent at the time our brains tend to automatically focus on sounds from within ourselves; such as heart beat in our ears. If thats not what you think it might be, it could be your soul departing the body preparing for an astral travel. I have loud chaotic noise when I return. It has been said that our soul will never get lost from the body and it is always connected with a silver string extending from our solar plexus. These are just a few of my thoughts for you.