Adam Clarke on Psalms 18:13

The Lord also thundered in the heavens, and the Highest gave his voice - And then followed the hail and coals of fire. The former verse mentioned the lightning, with its effects; this gives us the report of the thunder, and the increasing storm of hail and fire that attended it. Some think the words hail-stones and coals of fire are entered here by some careless transcribers from the preceding verse; and it is true that they are wanting in the Septuagint and the Arabic, in the parallel place in 2 Samuel, and in five of Kennicott's and De Rossi's MSS. I should rather, with Bishop Horsley, suppose them to be an interpolation in the preceding verse: or in that to have been borrowed from this; for this most certainly is their true place.