On the Lord's day, John heard a loud voice behind him like what?

Answer: A trumpet

John was in the Spirit on the Lord's day and heard a loud voice like a trumpet telling him to write to the seven churches.

“On the Lord’s day I was in the Spirit, and I heard behind me a loud voice like a trumpet, saying, “Write on a scroll what you see and send it to the seven churches: to Ephesus, Smyrna, Pergamum, Thyatira, Sardis, Philadelphia, and Laodicea.””— Revelation 1:10-11 (BSB)