Book of Joel Chapter 2 Vs. 5

 The Day of the Lord

Like the noise of chariots on the tops of mountains shall they leap, like the noise of a flame of fire that devoureth the stubble, as a strong people set in battle array. Joel 2:5

Like the noise... The motion of the locusts is leaping from place to place; for which the locusts have legs peculiarly made, their hindermost being the longest; wherefore Pliny observes, that insects which have their hindermost legs, are the long leap locusts.

To which agrees the Scripture description of them: “which have legs above their feet, to leap withal upon the earth; even those of them ye may eat; the locust after his kind” (Lev. 11:21).

of chariots on... There sound resembles the jumping of chariots on mountains and hills, which are uneven, and usually have stones lie scattered about, which, with the chains and irons about chariots, cause a great rattling; and the noise of locusts is compared to the noise of these, which is represented as very great.

Some say they can be heard six miles off as they make such a noise with their wings when they fly, that they are thought to be other winged fowls (see Rev. 9:9).

Like the noise... As they are before compared to fire, and a flame of fire that devoured all things as easily as the fire devours stubble, so here to the crackling noise of it see (Eccl. 7:6).

as a strong... That is, as the noise of a mighty army prepared for battle, just going to make the onset, when they lift up their voices aloud, and give a terrible shout; for this clause, as the other two, refer to the noise made by the locusts in their march. God's army is set in battle array.

There will not even be stubble left, because the 4 types of locusts even destroy the stubble. This is speaking of literally millions of locusts as stated in the Book of Revelation. There would be a deafening roar from their wings. This would leave the land in terrible shape, as if it had been devastated by a fire.

Nothing can impede the invaders’ swift approach. God's army seemingly leap over the mountaintops. The Hebrew verb for “leap over” (rāqaḏ) suggests both flying locusts and speeding chariots (on the latter, cf. Nah. 3:2, where rāqaḏ is trans. “jolting”).