John Gill Commentary 1 Kings 1:45

"and Zadok the priest and Nathan the prophet have anointed him king in Gihon; and they are come up from thence rejoicing, so that the city rang again. This is the noise that ye have heard." — 1 Kings 1:45 (ASV)

And Zadok the priest, and Nathan the prophet, have anointed
him king in Gihon
Or at Gihon; that is, Siloah, according to the Targum; here the act of anointing is ascribed to them both, as in (1 Kings 1:34); Zadok very probably applied the oil to him, and Nathan might be some way or other assisting in it; however he was here present, not only as approving of it, but declaring it as a prophet, that it was according to the will of God, as well as of the king:

and they are come up from thence rejoicing ;
with a multitude of people along with them:

so that the city rang again ;
with the blowing of trumpets, the sound of pipings, and the shouts of the people:

this [is] the noise which you have heard ;
which had so alarmed them.