at&t Note 4 text notification sound changes while in a call

[shizam76]

I have a doorbell sound programmed for notifications of text...and some other app notifications. If I get a call or make a call and a text comes in, instead of my normal doorbell notification sound, the phone plays the "whistle" sound. When I end the call and texts come in, my normal doorbell sound plays. It didn't used to do this. WHY and HOW could this sound change on its own...and then change back when not in a call???

Anyone else notice this??