Final Update:

So replaced upper wishbone, upper locating link, and wheel hub bearings in pairs.

Alignment was performed. I had the alignment checked when I first got it at 25,000 miles and the rear camber was at 1.5deg or so, which progressively got steeper over time to a bit over 2 deg. At my last alignment at 40,000 or so (after front suspension work), the best we could get rear camber to was 2-ish deg.

I was glad to see we could now get rear camber back to 1.5deg. Toe front and rear was set to around .05 or so.

Went out for a test drive and I'm glad to hear (or not hear) the "running on a steel bridge" sound is gone!

Looks like it was the rear wheel bearings as many have shared.

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04 X5 3.0i auto
03 X5 4.6is