I have it in my brand new 2019 Limited since May. It's a definite problem. I use an iphone 8 and I do have the JBL system. Taking it to service today.Weird. Happened to me today also. I have had my 2019 about 3 weeks, but this may have been my first call in it.
My wife has a 2019 Limited and had this problem. Easy fix.
The phone has a "bluetooth" volume that's separate from the normal volume (all versions of iPhones do this + most Android phones.)
Because the bluetooth volume was turned down, she had to turn up the car volume to hear people speaking, and at some point it gets picked up by the phone mic.
Solution is to start a call, turn the phone bluetooth volume all the way up, then adjust the head unit audio down. Problem will go away.