What is cause ofwhining/screeching engine sound when stopped at traffic light

What is your question?

Engine whines, descends from high to low sound, when coasting (no gas pedal, no brake) in reverse, coming to stop at traffic light especially noticeable in cold weather. Used to be occasionally, now every trip. Complained about something similar 70K miles ago. Paid for an “air pump” repair. Dangerous, inefficient or just annoying?