Audio problem: After the mayor tells Andy that his three daughters will be in The Beauty Contest, Andy phones Ellie and when she hangs up on him we hear Andy say, "Hello? Hello?" but we see him only mouthing the second hello.
The Statue - S7-E23
Audio problem: When Aunt Bee is introduced at the start of the ceremony, in the first wideshot as she begins her speech we hear her say, "Friends, neighbors, and fellow citizens of Mayberry" but it's not in sync with her mouth movements. (00:18:45)
Opie's Group - S8-E9
Audio problem: The band Opie is in has two guitar players but no bass player, even though you can hear a bass guitar being played.
Answer: Those "boxes" are valences that used to be very common, before air conditioning. They allow for windows to be open during rain storms. They permit air circulation, without letting the rain in.