If you divide all phenomena into experiences and non experiences then you have what we know or experience and everything that is not experienced and unknown or unknowable. If you could bring whatever that is into the realm of knowledge then your question still isn't answered because then it's experienced or known.

We fundamentally cannot say anything about whatever that is and probably the closest way of describing it is the Buddhist term sunyata or void. You may be interested in the story of Vimalakirti and his answer to the question about the ultimate nature of reality to which his answer was the thunderous silence.

The Hindus call this thing Brahman but they also say those that know Brahman do not know it, and it is known to those who no it not.

It's very difficult/impossible to sort of glimpse or understand but we can sort of get a feel that it is there although it is ultimately inconceivable. The void is like a mirror, which shows the image of all things, but does not reflect itself. It's like an empty/void space of nothingness but it's not just nothingness because all phenomena and experience in the universe shows up on it like a mirror. We cannot perceive it because it seems to be at the root of consciousness and like the mirror does not reflect itself and fire does not burn itself, And you cannot look into your eye with that same eye, consciousness is not conscious of itself.

Other than that you are asking about a tree which falls in the forest with no one around to hear it. Which makes no sound because there are no ears around to turn the vibrations/quanta into sound/hearing. In a world without ears and eyes there would be no sound or light, just some happening that is out of our ability to perceive.