Ok, this ended up being a problem with the caliper bushings! There was an uneven buildup of rust around the outside of the bushings holding the caliper kind of cocked and sticky. The noise was all from the caliper and transmitted through the spring!

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)