AirPods Pro 2 digital sound

I’ve had my AirPods Pro 2 with USB-C for a few months and recently noticed something odd. Whenever I put the AirPods back into the case to charge, they make a soft, low-volume digital sound. It’s not the usual charging “ding” you hear when you plug in the case—it’s something else entirely. Am I the only one who’s picked up on this, or is this a well-known thing?