I "rotated" my tires RR --> FL and RL --> FR. I have staggered setup so ended up with the 10" wheels on front. Tire size is same on all 4, just the rims are staggered.
Had some terrible vibration on braking. Just terrible. Moved the 10" rims back to the rear end and all became good again.
Try rotating your tires and see if anything changes.

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2004 X5 3.0