Mine makes a similar sound at low speeds - frequency proportional to engine speed. I think my issue is worn belt tensioners on the serpentine belt. I plan to replace belt, idler and tensioner during the next few weeks.
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F10 530d M Sport, September 2012 Individual Amazonite Silver, Oyster Dakota Leather, Auto, Nav Pro, Bluetooth + USB Devices, Expanded BMW Online, Comfort Seats, Sunroof, Sun Protection Glass Individual Satin Walnut Honey Brown Trim Interior Inside/Outside Mirror with folding and autodip, M Rear Spoiler
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