Hmm... When in deep meditation I have heard sound and voice, but I usually attribute it to either my inner voice (thoughts bubbled up from the subconscious), or information from my spirit guide. Depending on the tone and energy behind it. Chances are pretty good this is what might be happening for you as well. as you reach a deeper state of focus and meditation it clears away the mental background noise that usually drowns out other inner thoughts or information.