The Lord also thundered, to wit, against my adversaries. Thunder is a sign of God's anger, 1 Samuel 2:10, 1 Samuel 7:10. His voice, i.e. thunder, oft so called. The same thing expressed in other words.
Related Commentaries of Psalms 18:13
Psalms 18:13
13 The LORD also thundered in the heavens, and the Highest gave his voice; hail stones and coals of fire.