Yea, FSU on my 5 caused the same thing. Install is pretty easy. From the TIS it looks like the install is the same on the X5 as it is on the e39.
It looks like you fixed it ,but roughly:
Remove the black plastic panel under glove box (there's a screw and a pair of twist plugs that hold it on on the X), disconnect the light
Remove the carpet trim on the pass side of the center console (there's a screw towards the front and then it will slide out)
Lay contorted on your back, unclip the FSU harness and release the tab holding it in. It is kind of a bitch. It is also somewhat further in/up than pictures seem to indicate.
Big drain on the battery while the alarm is on will cause alarm to go off (blower, dome lights).