I think I figured it out--it is the Surface app from Microsoft Store. After uninstalling it the beeping stopped. Verified on two different machines. Hope this helps!
UPDATE: after some more poking around I am no longer sure the Surface app is to blame. It seems like the beeping does not occur after fresh system restart. Once I turn the headphones off and back on, the beeping often returns.
That said, I found a workaround that seems to work reliably so far:
- Open Settings app and choose "Bluetooth and devices" tab
- Turn off Bluetooth.
- Wait for the Headphones to announce they have disconnected from your machine.
- Turn Bluetooth back on
- Reconnect
The beeping will be gone till the headphones are shut off.