Loud, frequent whine/groan from engine area?

I have two videos to hear what the sound is from inside the vehicle and from outside with the hood up. For additional information, the noise happens after the car has warmed up and only happens when I've released the gas pedal. If I'm idling in place or driving down the road it always happens when no gas is being added to the engine. Never heard a noise quite like this and haven't had any luck finding any video with a similar sound online anywhere. Also, no check engine light has come on yet.