I found a significant source of wind noise at the top of the door pillar trim on the exterior. There's a gap there where the seal had deteriorated. I couldn't figure out how to properly take it apart without a ton of work so I took some closed cell foam rods and stuffed it in the gap using a trim tool. I broke the foam into small pieces and packed it until it was full. It's not visible from the outside and helped a lot.

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2003 X5 3.0i MT, White, 161k