EmpressInYellow
Banned
Ah, I also noticed this but I wasn't sure if it was just me or not.
I just went back and checked, and in previous episodes:
The same basic synth-y noise is used when Lion is teleporting (in, say, "It Could've Been Great"), when the big diamond cataclysm happens in flashbacks ("Same Old World" and "Monster Reunion") and when Peridot uses the diamond communicator ("Message Received").
Could mean nothing! Could just be a particular style of effect being re-used. But it seems pretty specific.