Clearing your mind of all thought? <giggles> That's sort of like hearing no sound or seeing no sight...but I think I understand what you mean. Medititation is the brains' worst enemy. Being ego orientated it wants you all wrapped up in yourself. Buddha, when medititating, would ignore even the most brilliant visions as mere distractions....next time, move past the voice and you might just be surprised.

P.S. But if you start to hear voices on a regular basis, see a Dr. quickly! lol

Peace!