Moses does not tell Joshua of the divine communication that had been made to him respecting the apostasy of the people, but only corrects his impression by calling his attention to the kind of noise which they are making.

Joshua - said - There is a noise of war in the camp - How natural was this thought to the mind of a military man! Hearing a confused noise he supposed that the Israelitish camp had been attacked by some of the neighboring tribes.

And when Joshua heard the noise of the people, as they shouted,.... Dancing about the calf: when Moses went up into the mount, Joshua went with him, and tarried in a lower part of the mount all the forty days until he returned, see Exodus 24:13 though not so low as the bottom of the mount where the people were, nor so near it as to know what they did there, for of their affairs he seems to be entirely ignorant; nor so high as where Moses was, or, however, not in the cloud where he conversed with God, for of what passed between them he had no knowledge, until declared by Moses:

he said unto Moses, there is a noise of war in the camp; such a noise as soldiers make in an onset for battle; he supposed that some enemy was come upon and had attacked the people, and that this noise was the noise of the enemy, or of the Israelites, or both, just beginning the battle; or on the finishing of it on the account of victory on one side or the other; and as he was the general of the army, it must give him a concern that he should be absent at such a time.

And when Joshua heard the noise of the people as they shouted, he said unto Moses, There is a noise of war in the camp.

32:15-20 What a change it is, to come down from the mount of communion with God, to converse with a wicked world. In God we see nothing but what is pure and pleasing; in the world nothing but what is sinful and provoking. That it might appear an idol is nothing in the world, Moses ground the calf to dust. Mixing this powder with their drink, signified that the backslider in heart should be filled with his own ways.