Why does my Google pixel 3 xl do this?

When I try to make a phone call and it makes the ring that all phones do while you are waiting for the recipient to answer on the other end, it starts off loud, then goes to a quiet ring. Why is this? I noticed it does the same thing in speaker as well. Why does it do this and how did I fix it? Is this just a normal feature for Google pixel phones?

2017-04-11T00:37:33.809Z