Hi Ken,
It took me awhile, but I got mine to stop rattling. I did use some blue silicone around on each and let it dry (I used a very thin bead which is not noticable when installed. The most important thing I did was the installation. I found I could lay the wheel on the cap, carefully, and if I raised one side of the wheel, it would allow me to further tap the tabs down. I kept doing this until I didn't see any further progress. I used all the tabs. Using this method, with patience, I was able to get each pretty secure....then, the fininshing touch. With the wheels back on the vehicle, I turned the caps that needed a little tightening. On mine, a little twist made them really snug. No rattles yet.....we'll see.