Ok, here is the issue.
I installed a "AUX input" to my truck radio. I stream internet radio with TUNE IN app. When I get a call, I answer it, and the radio keeps playing for like 5 seconds. The person calling me can hear the radio playing of course. I used to stream the music to my radio through a BT device before adding the AUX plug. This never happened then.
Is it an issue with the switch from BT AUDIO to Line out AUDIO, or something in the app that changed? I think I've also had one or two TUNE IN updates in the mean time.