I have a 2018 High Country. About a month ago it started developing a vibration/rattling kind of noise on startup and speeds from 0 to about 50 mph. Took it to Christian Brothers Auto Repair, (I highly recommend them), and they found that the exhaust pipe bracket was broken. They included a video of the problem plus a written explanation. I can't add the video, but have included a screen shot of the broken bracket, along with their explanation. The repair took about an hour.
From CBA Technician: "Test drove vehicle and could hear a metallic rattle. Got vehicle on the lift and checked for any loose components and found that the flex exhaust bracket is broken. Causing upon acceleration for the flex exhaust pipe to rattle around. Removed broken bracket and noise is gone now."