I was getting annoyed by all the clicking and popping as the X bounced over our crappy pavement and hunted down the source.

In our case, it was the weatherstripping on the door openings (mounted to the body). There is a lip that overhangs the interior trim pieces, and during assembly, it gets, I dunno - bunched up. Basically, as it's pressed into place, the friction of the rubber on the plastic trim makes it bulge up. I pulled the weatherstrip off a section at a time, and refastened it, making sure to put pressure at an angle so that the lip lays flat and the weatherstripping seats completely.

All clicks are now long gone! So if you have clicks/pops in your new X, coming from the sides of the truck, spend a few minutes and re-seat your weatherstripping. Costs nothing, and in my case, paid off massively.