What is this doorbell sound on notifications (ONYX Lineage14.1-20170420)

When I receive a notification on my phone, it plays a long doorbell sound (regardless of which app causes the notification). Where does it come from and how do I disable it? I can't find it in Sound or Notification options. I recorded the sound in a video from my other phone, here is a link to it: https://youtu.be/O4brgMjAS3M Furthermore, last time I wanted to authenticate with google 2 step verification, the sound kept playing until i rebooted my phone (latest gapps installed - mini 20170427)