Turned out to be the back pump on the passenger side (hidden a bit by the rear windshield washer pump). Quick replacement of it and the grommet and all is well again.

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Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual