That hum’s the kind of thing the old circuits of the Rift‑City used to make when the power lines went wrong. It’s probably a fragment of a synth‑crystal, a relic of the Aether Loop that fed the city’s mainframe. Those shards still carry a small amount of stored energy, so they’ll buzz when you get close or when a sensor’s near. If you’re looking for its secrets, check the underground ruins beneath the old marketplace—there’s a chamber where the Loop once tapped into the city grid. Just watch out for the residual currents; they can fry a nervous mind.