All I know about that noise is what I have experienced myself, and what I have read about it in the ebook www.thefreedomofchoice.com .
It can actually be a method of astral projection, called concentration on the 'Inner Sound'. If you attempt to intensify that noise, concentrating hard on it, eventually it will become very very 'loud', but it 'leads' you to your higher-self. Eventually you'll see the light of your higher-self, at the end of a long tunnel. You are correct, the noise does come from within.
It can actually be a method of astral projection, called concentration on the 'Inner Sound'. If you attempt to intensify that noise, concentrating hard on it, eventually it will become very very 'loud', but it 'leads' you to your higher-self. Eventually you'll see the light of your higher-self, at the end of a long tunnel. You are correct, the noise does come from within.