I went through this about 16 months ago with a similar issue and here's what was wrong with my 2005 X5. My right rear lock actuator was found to be faulty. Apparently, the locking mechanism was slipping in and out of a fully locked position thereby triggering the alarm. An occasional 'door open' would light up on the dash, a clue that helped pinpoint the problem. So they replaced the lock assembly. They also found the Module faulty and replaced that too. Did the trick. Haven't had an incident since. Hope that helps

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2005 X5 4.4i with SP, PP, CW, RC, Prem Sound, DVD Nav, Comfort Seats, Style 87 Wheels, Alum Running Boards, Sirius Sat, 6-cd Changer.