Airpods Pro 2 makes ascending beeping noise

For the last couple of months, my AirPods Pro 2 has been periodically making a low-volume 4-beat ascending beeping noise. It almost sounds like a cartoon computer "powering up". It happens once every couple of days and seems to happen randomly. I have just been able to figure out that it is coming from my AirPods because it is so soft. It lasts about half a second, but I want to know why it happens. Is anyone else having a similar experience or knows why it is happening?