On a quantum scale everything is random. In that case, true randomness exist. Though being a far-fetched idea, Bell’s theorem explains this well:
No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics.
As far as we know, there is nothing in the universe that exceed the speed of light. So it is okay for now to say that the quantum events like a radioactive decay of an isotope is close to true randomness and there are no hidden variables known to us that can predict it. Beyond this point, the scope falls into a metaphysical state and questions the validity of the quantum theory.