So I have a 21 bighorn with 5k miles. Was driving one day and kept hearing this rattle from the drivers side b pillar. I pulled over and noticed the pillar cover is slightly loose. Well, a few days later I was driving and had the kids in the back and on the same road and no rattle. Having ocd to interior noise I went back to this road without the kids and guess what.. the rattle came back. I pulled over and inspected the interior and it hit me! The rear seatbelt was vibrating on the c pillar. I buckled the rear seat belts and the rattle went away.
So if you hear a rattle that sounds like it’s right next to your left ear from the b pillar, try buckling the rear seat belts!