Canon EF 70-200 F/4 IS USM - Amazon Trade-in: loose cylinder & Rattle

I just received by lens back about an hour and a half ago from Amazon.

I inspected the outside carefully, there were no major cracks or dents.

I could not detect what was described as a loose cylinder.  Thus, I have no idea what they meant.  I could detect what one might describe as a slight rattle when I shook the lens gently in my hands.

However, once I put it back on my 6D and powered it up, the lens immediately resumed correct operation. The AF works, the focusing works near and far, the zoom function works, MF works. There is nothing about this lens that doesn't work.

My thoughts are that the so-called inspector is simply not competent and he or she would have used the lens on a Canon camera instead of trying to manipulate it off the camera. I suspect that the rattling sound inside must have something to do with the image stabilization system, which must somehow float while the user is handholding the lens. Whatever does that may rattle slightly when the lens is not on the camera and powered.  I never shake my lenses looking for rattling noises as I see no reason to do that. Also, I don't think I ever zoom or focus with the lens off the camera, either.

I was hoping that others here would have some experience with this behavior on IS lenses. Several months ago I read a post on facebook from a guy who was having the same issues with a Canon EF 100-400mm Mk2. This fellow even made a video on it.  It was hard to believe how his brand new lens was behaving but it righted itself once he put it back on a camera.  I would post a link here but I cannot seen to find the post or the video now.

I hope this experience will help someone else down the road and I still would like to see some discussion on this possible behaivor of these IS lenses.