I used to have casette tapes. So, I'd remove the the tape from the casette and turn it over. Put it back into the casette and when i press play, it's all backwords. If i'm lucky, then i might hear something that might sound 'satanic'.
But I feel all these 'messages' were actually put in by the recording companies themselves, to get impressionable teenagers (like how I was) to buy the records.