Contradiction with John 1:18
John claims that no one has ever seen God, while 2 Peter 1:18 describes hearing the voice of God.
John 1:18: No man hath seen God at any time; the only begotten Son, which is in the bosom of the Father, he hath declared [him].
Contradiction with Acts 9:7
States that men with Saul heard the voice but saw nothing, somewhat conflicting with the clarity of the account in 2 Peter 1:18.
Acts 9:7: And the men which journeyed with him stood speechless, hearing a voice, but seeing no man.