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The fact it's turning up gibberish when transcribed shows there's almost certainly something else at play with the morse. If it's encrypted with something further like a caeser cipher, bear in mind that the pigpen clue was "YOU ARE THE KEY YOU KNOW IT IF YOU LISTEN". If this were another layer of encryption, perhaps "you" or "u" could literally be the key to use in the cipher.
It could also be reversed as people have mentioned. Apologies that my pals didn't provide anything quite as concrete as we'd hoped. They gave it a good thrashing  |
I think "YOU ARE THE KEY YOU KNOW IT IF YOU LISTEN" may apply to any dialogue and sound effects within the audio clip. Maybe that could lead us to a clue for solving this.