Here's what we know about the mysterious transmission:
* It's related to the events of the original Gold and Silver games. It's heavily implied that it's the same transmission that was used by the legendary beasts Raikou, Entei, and Suicune to communicate with their trainers.
* The transmission is very cryptic. It's a series of beeps, chirps, and distorted sounds that are impossible to understand without further context.
* It's tied to the locations of the legendary beasts. You can hear the transmission more frequently in certain areas of Johto, especially near the locations where you find the legendary beasts.
* It's eventually explained. If you catch all three legendary beasts, you will hear a more clear version of the transmission during the final battle with the legendary beasts. This final transmission reveals that it's the sound of the legendary beasts calling out to their trainers.
In conclusion: The mysterious transmission is a spooky, intriguing element of the game that adds to the mystery of the legendary beasts. It's a clever way to tie the game's events to the original Gold and Silver games, and it keeps players guessing until the very end.