I'm having trouble formulating my exact thoughts in this post, bear with me. I hope you can understand my meaning.
When you know someone really well their voice leaves an imprint on you. You KNOW their voice, you understand it's distinctness, can pick it out of chaos, it's part of you forever.
I remember, distinctly, in high school I heard one of my very good friends, Becky, cough. I wasn't looking for her, but when I heard that cough I knew who it was just around the corner. She laughed when I told her I found her because of her cough. But my heart knew that cough.
Years later I was teaching Sunday School, the nursery was in the next section of the 3-in-1 room, separated by those accordion dividers found in pretty nearly all LDS churches, and I heard Mr. M giggle, it wasn't an uproarious laugh, it was just a simple giggle. I told my class that that was my son laughing. They were all amazed that I picked that laugh out of all the others. I knew he was there but I wasn't expecting to have contact with him for two more hours. He is my son, I love him everyday and my heart knew that laugh.
Watching a home video from at least 22 years ago, there was my mother, not on screen, saying 'It goes this way.' I was watching the video for the express purpose of hearing her voice again after at least 8 years of not having her with me, I didn't even know which sentence she was going to speak. I was anticipating the sound I knew so well: the voice of the person who brought me into life, my heart jumped, it knew it was her..
3 Nephi 11:3 And it came to pass that while they were thus conversing one with another, they heard a voice as if it came out of heaven; and they cast their eyes round about, for they understood not the voice which they heard; and it was not a harsh voice, neither was it a loud voice; nevertheless, and notwithstanding it being a small voice it did pierce them that did hear to the center, insomuch that there was no part of their frame that it did not cause to quake; yea, it did pierce them to the very soul, and did cause their hearts to burn.
I hope that when I hear His voice again, I will know that voice, because my heart knows Him.