The answer is on Apple's support page, which reads: "To help ensure that your AirPods microphones and speakers are operating at their best (for example, to help provide high-quality hearing test results), your AirPods may periodically play a quiet chime when they’re in their charging case."

If you've been hearing a chiming sound from your AirPods Pro 2 case when the AirPods are charging, it's a feature that Apple added with

A strange noise irritated owners of the AirPods Pro 2 and the discussion is now mainly about Apple's communication.

Macworld Back in 2022, Apple added a speaker to the AirPods Pro case to help find it when lost in a couch cushion or under a desk. But for years people have been hearing their cases make sounds all on their own.