Phone makes ding noise during calls?

So, I have a iPhone XR. Nothing wrong with it working, but when I am in calls (I use my phone to call friends every night and join class sessions) I have a ring alert and it just has 3 ‘ding ding ding’ noises in a row and it goes from high to low. It’s not any notifications, and there’s no search answers about this. I’ve checked everything I get notifications on, and nothing. Is there a source of this sound or atlesst a explanation? I’d like to figure it out.