I had something similar from Wild Rides. No need to weld them in, but it wouldn't hurt.
Jeff, did you paint those parts silver? You always have to cut the '94-'04 lower torque box openings to get those parts in. Doesn't look like you 'clearanced' the spare tire well. That pop is probably from a slight binding-up of the control arms or just a little movement. Don't get me wrong, the install looks good. Just trying to help. Can't wait to see how it runs.