In the 80s Fr. John O'Connor was one of the first priests to expose, among many other things, backwards masking, saying that even the term "Rock and Roll" has in it's nature, sɛҳuąƖ connotations. I believe that was in his talk "Hell's war on our children". There used to be plenty of youtube videos playing songs backwards proving beyond a doubt the messages are put there purposely.
He is an outstanding speaker worth listening to: