Does the case look a little different? See my Blog Post, Side Case Touchup.
Anyway, today I got focused on isolating the rattle.
The cases have three points of attachment on the motorcycle. The locking mechanism is in the upper forward point of attachment. The only buffered point of attachment is the lower forward point. That is, the two upper points of attachment are plastic-on-plastic.
The corresponding attachment points/post on the case (using the left case) are reflected in the following photo.
With the cases installed on the motorcycle, I carefully wiggled them to see if I could isolate from where the rattle was being emitted. It was clearly the rear point of attachment. The lower forward point was very secure and is buffered by the rubber attachment block. The upper forward point of attachment, even though not buffered, was also quite secure once locked. The only movement was from the rear post as shown in the photo below.
After trial and error with a number of different materials and thicknesses, I found that only a very thin buffering medium was going to fit between the rear post and its point of attachment on the motorcycle. I ultimately was able to fit the soft side of some self-adhesive Velcro strip.
I first put some of the strip on the very front of the post (over the orange triangle). That helped a great deal, but did not completely cure the rattle.
I then put another strip of the Velcro on the side of the post (facing motorcycle). Bingo! Now the cases go on securely and do not rattle at all. Case solved! (no pun intended)
Be advised that with those small strips of thin Velco the cases are now very tightly installed. Normally, installation and removal of the cases requires a little bump from the heal of your palm. It now requires a good deal of bump. I would caution (both without or with this mod) that the bump should be applied only to the back side of the case; not the cover the case. Given how tight the case is now installed, I'm concerned that a good bump on the cover could end up damaging the case hinges or other parts. So USE CAUTION installing and removing the cases (even if you don't do this mod)!