some time ago, while floating in a sensory deprivation tank i had the distinct experience of hearing crickets chirping in my ears. Later i would find myself waking up to the sound only to discover that it was inside my head, not outside my window.
After some research, i found this book : The Law of Attention by Edward Michael. It is about the practice of Nada yoga, which is training yourself to listen to your own inner sounds. Everyone has them although most of the time we are oblivious to them, the idea is basically to learn to use the sounds to anchor you in the Here and Now. here is an excerpt from the book
" with the aid of this mystical sound, the aspirant will have a better chance of remaining vigilant and connected to his inner Source, abiding for longer and longer periods in a state of self-recollectedness. He will ultimately come to see for himself that he is conscious of his existence solely during moments when he feels this state of inner presence. The rest of the time, when he is in his habitual state of oblivion, he feels his existence little and - according to the degree to which he is absent - may even have no awareness of it at all."