Audio problem: When the very first song ends during the Festival scene, keep an eye on the guitarist to the right. His hand is still moving but no sound is coming out of his guitar. (00:56:55)
Audio problem: When Mad-dog Tannen is standing over Marty, who is playing possum, you see Tannen cock his gun twice between two shots, although there is no sound effect for the first time. (01:27:50)
Answer: Someone would go into his barn and do what? See a sign that says time machine and believe it and then use it? Seems highly unlikely.
lionhead