On my 2003 I found out that all the doors lock except for the hatch.
It's really loud when I depress the release push button.
I can open the hatch even when all other doors are locked.

Not sure where to start looking.
The hatch clasp mechanism opens and latches the hatch.
Only opens when the button is depressed.
Doesn't pop open inappropriately.
It just doesn't lock preventing entry.

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2003 4.6is X5
2003 525it