Ok, it turns out the whining noise is coming from the transfer case- indie put car up on lift and ran it. They recommended replacement with new for $4,000 (parts+labor). However, I'm considering installing a used one instead. Or myself doing draining and refilling and see if that makes a difference before coughing out 4 grand or so.

Any thoughts or experience with above options?

Thanks!

X5 4.4 sports 2005, 92k miles.

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.