Weird Noise Under Deceleration

[SteffR]

Hi All,
So I have a whining kinda noise on X5 E70 2011 40D that only happens when decelerating, in gear or neutral, no change.
Does not change speed or pitch regardless of up or down shifting manually.

I had fluids changed in TC , front rear diffs and gearbox. No Change.
I pulled fuse for Transfer Case, and it goes away.

I figure that pulling fuse only stops drive from TC case forwards, so doesn't necessarily mean TC.

Has anybody any ideas before I start replacing expensive items?

Thanks
Steff