“And they that were with me saw indeed the light, and were afraid; but they heard not the voice of him that spoke to Me” (Acts 22:9).
Some may think that this is a mistake in the Scriptures, because in Acts 9:7 Paul said that those who were with him heard the voice. However, John 12:29 gives us insight into what God’s voice sounds like. People heard His voice but thought that it thundered (see also 2 Samuel 22:14; Job 37:4,5; 40:9). They obviously heard it but the words were not coherent to them. [From, The Evidence Bible]