There are multiple post about this in this Forum. Someone used some packing foam and used it between the headliner and the metal structure onto wich it's supposed to be glued. apparantly the fix worked.
My car went in twice for it and both dealers failed to correct the rattle. I'm about to take matters in my own hands and fix the damn thing myself. Not impressed by the service quality offered to fix this...but I'll stay on the topic.
Do a search and you will find multiple post about it. With some luck, you'll find the poster who found the fix and see how he fixed it.
2012 Oxford White SEL Sedan
303A + winter package + Moonroof + 16'' OEM