I was just giving my Raven a second clean ( see Dan, I do take heed )
What have I done?
Matt, all rims have joints (or "joins"), though some are welded and the joint has been ground and finished in such a way as to be nearly invisible unless you look into the rim well with the tire, tube, and rim-strip removed. Rims are formed (bent) from straight sections of extruded aluminum, then joined at the ends so they form a hoop. Often, rims are not welded, but instead use pins (in each sidewall) or a slug (in the center) that is either an interference fit or held in place by the spoke ferrules. Spoke tension draws the ends together, helping close the joint and make it secure.
Usually, when rims have joint problems, the rim "ends" are offset or not quite jointed completely together, making for a little bump that is found by the brake pads; extremely annoying when one applies the brakes and hears/feels "thup-thup-thup".
Best,
Dan.