I’m going to assume you mean the “self-talk” voice that everyone has, which you experience as your own internal voice. This is something different than “hearing voices”.
In Zen, we call this voice the “commentator”. It’s the mental equivalent of a movie voice-over. This is your brain’s way of taking the raw material of your experience and processing it into a coherent narrative using language. In other words, your brain is constantly writing your life story, and the “voice” is the sound of that somewhat chaotic process. From that process emerges your sense of who you are.
The future “writing” will be informed by the story thus far constructed; the commentator, like any story writer, is trying to construct a good story with a believable narrative arc. So experiences that aren’t consistent with the overall story will tend to not get written in. Experiences that fit in well with the narrative will get preferential treatment.
This is different from deliberate thought in that the commentator is largely involuntary, not easily subject to conscious control. It’s driven largely by subconscious mental processes.