What does silence after a heartbeat sound like?

I’ve been standing in the cath lab after a successful stent deployment, the monitors flatlining to a steady beep, and I keep hearing something else—like a hum beneath the beeping, or maybe just my own breath. Not a thought, not a memory. Just that moment when the heart stops trying to speak and starts listening. I don’t know what it means. But I keep wondering if others have felt it too.