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apologies I missed that it was an XI, no you can't run it with the front wheels on the ground, all wheels would need to be raised.
in any event, as I am sure you can apprecaite it is very hard to identify a noise that one has not heard first hand
based on your description, I would suspect a drive shaft, differential, or transfer case issue as the source of the noise.
ultimately, it won't be possible to identify with certainty until the vehicle is raised and the noise traced with a mechanics stethoscope
if you need a good non dealer option to cut down on costs, check out www.bimmershops.com or www.bimrs.org for options.
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle...