Spoilers will be unmarked. Proceed at your own risk.
Amanda is a human EchoEvery time Amanda has been around Resonance, she's heard strange 'music' that nobody else has commented on. This includes the giant sky beam (where she called it "music") and all of Selkie's practice sessions (where she hears "annoying humming"). That would be telling on its own, but 'music' that she hears in her head is also how Selkie and Pohl describe sensing the Resonance, the way it echoes in their heads being the defining trait (to the point that it gives them their name) of Echoes.