Sometimes, a loose rib is indicative of corrosion between/under the ribs. If that's the case, It's usually detected when the rib(s) is/are removed. Then, cleaning and re-tinning and re-soldering is the better way to go,IMO. Among the well respected gunsmiths, there seems to be enough of them that say they'll only do ribs if they pull them all and clean and relay all to ensure a good job, that there has to be something to it at least some of the time.
There have been numerous cases posted on this bbs that were not cases of prevalent corrosion under the ribs and a simple repair without pulling the entire rib seems to have solved the problem.
Me? I'd like to pull the ribs to make sure it won't come back anytime soon.