Simply, the voice you produce to speak out loud is different than the voice everyone else perceives when you speak. The reason being the difference in perception between yourself and anyone else listening. When we hear voices from others, those sound waves go directly into the ear, hitting the ear drum and producing vibrations which then gets processed into sound. As an individual speaks, while they are speaking, their ear drums vibrate not only from the sound waves, but from the vibrations we emit while speaking. The movement involved with producing speech causes vibrations of their own to create that sound like the vocal cords vibrating as we speak. Thus affecting our ability to process the sounds we produce; altering perception.
The combination of sound wave and body vibrations has the effect to make your voice sound much lower and more rich. So when hearing your voice, without those vocal cord/body vibrations it often sounds foreign and unpleasant. This is why we hate the sound of our own voice.