Cause and Solution!
FYI, my truck is a 2017 Chevy Colorado. Nevertheless, the noise I was hearing matches exactly what you all are experiencing.
It appears as though my problem with the issue may finally be resolved. I attached service notes from the dealer. But in a nutshell: Near the B pillar pass through connector, there are two pieces of sheet metal sandwiched together that were causing the rattle. There should be a small amount of space between the two pieces, but there wasn't enough. Which is probably why I only heard the noise during warmer weather, as heat causes expansion. The techs at the body shop injected some 3M foam in the area of the B-pillar pass through to eliminate the two pieces contacting each other.
I folded a hand towel in half, wedged it over the door seal on the back side of the pillar, and then closed the rear door on it. Being that the noise is intermittent, I can't be 100% sure, but since then, I've yet to hear the ticking noise. Obviously not a permanent solution, but...