I have a 2001 X5 since day one. I remember I had this annoying problem with the rear hatch opening by itself. I did get it fixed and there is a TSB about it in the dealership.

Apparently, some X5 were made with slightly tight wiring harness (i.e. harness slightly too short or not enough slack). The wiring harness goes through the right upper black rubber boot....(open your hatch and look at the upper right hand side). There are plenty of wires inside the boot....what would happen is one or some of the wires would chafe against that area and it would short itself and cause all kinds of funny things like popping the rear hatch on it's own or have your rear wiper/washer go on by itself....

So double check the wires and if there is a break on the insulation, then wrap it with electrical tape.

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