Acts 22

As Paul addresses the mob in Jerusalem, he recounts -

"...as I made my journey, and was come nigh unto Damascus about noon, suddenly there shone from heaven a great light round about me.
7 And I fell unto the ground, and heard a voice saying unto me, Saul, Saul, why persecutest thou me?
8 And I answered, Who art thou, Lord? And he said unto me, I am Jesus of Nazareth, whom thou persecutest." (New Testament | Acts 22:6 - 8)

What is interesting were -

"...they that were with me saw indeed the light, and were afraid; but they heard not the voice of him that spake to me." (New Testament | Acts 22:9)

This would suggest to me that in many visions, the voice of the Lord is not an audible voice, but a small voice directed, to what I would suggest, ones mind. The prophet Enos recounts -

"...there came a voice unto me, saying: Enos, thy sins are forgiven thee, and thou shalt be blessed." (Book of Mormon | Enos 1:5)

Much like Paul, Enos testified that a voice came 'saying" to him. As he continued in prayer for his bethren, Enos again testifies -

"...while I was thus struggling in the spirit, behold, the voice of the Lord came into my mind again, saying..." (Book of Mormon | Enos 1:10)

This would suggest that the voice of the Lord is not necessarily an audible voice. We also learn that shortly before the appearance of the Savior in the Americas, as the people -

"...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." (Book of Mormon | 3 Nephi 11:3)

Again we learn that all did not hear for Nephi recorded that th small voice did pierce them that did hear. As we read the scriptures, things may not be as we would logically think.