Note 6 at Joh 12:28: This was the third time recorded in the Gospels that the Father had spoken in an audible voice to or about Jesus (1st - at Jesus' baptism in the Jordan River, Mt 3:17, Mr 1:11, and Lu 3:22; and 2nd - at the transfiguration of Jesus, Mt 17:5, Mr 9:7, and Lu 9:35).

This verse makes it clear that it was a voice that the Father spoke in; however, there were different reports of the same event. Some people heard a voice and thought it was an angel who spoke; others thought it was thunder (Joh 12:29). This illustrates "the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned" (1Co 2:14). Carnal people with hardened hearts (see note 10 at Mr 6:52 and note 3 at Mr 8:17) will always find some natural explanation for the supernatural even if they hear an audible voice from God.