I just got my X5 back from the dealer and they adjusted the catch so that the hatch closes tightly. I have to close it with a bit more force now...but it doesn't rattle at all, which has made a huge difference. It has taken a bit of practice to get it to close every time (a few times it has closed, but when I get back into the car the light on the dash is on indicating that it is open.) I have a feeling that the rattle will be back over time though....not sure why but it just seems like it may work itself loose again.
BTW..this was covered under my CPO warranty.