The answer involves the Big Bang—an enormous chemical reaction which is thought to have been the very start of our known universe. It's common knowledge within scientific fields that the mentioned chemical reaction would create a massive amount of radiation, some of which lingers to this day. When you use a radio or television, and tune it to a frequency which coincides with the lingering radiation, you will hear static. This is the sound of the Big Bang remnants.
Now, armed with this knowledge, we can begin to theorize as to why we hear faint static in our heads sometimes. Perhaps our brains operate as an organic radio, each with a particular frequency. This would explain why we sometimes hear this static sound.
Our brains are receiving the leftover Big Bang radiation, and our brains hear it as static. Perhaps this could also be the solution as to how some "psychics" can read our minds. Perhaps their brains have the ability to convert the static from other peoples thoughts, and turn them into understandable information—something normal people have yet to be capable of.
Now, what is the possibility that this static we hear is in fact messages from God, which we have yet to decipher?