Pinbox moves?

A friend has a Jayco 5th wheel that's about 4 years old and noticed that the pinbox seemed to move up and down over bumps. He couldn't remember ever noticing this before. Suspicious that something wasn't right, he raised and lowered the trailer off the truck and measured that the pinbox moved up and down 1/2 inch from the cap of the 5th wheel. He says it doesn't seem to pull any differently but I don't think this is normal. I'm no expert but it seems to me that the pinbox should remain firm with the trailer and not move, even slightly. Sounds to me like the pinbox is loose or broken away from the frame work of the trailer. Unfortunately, you can't see up in there without removing all the paneling around the pinbox which isn't as easy as it sounds. Does this sound like something serious?