I have the same kind of noise and I think it is coming from the plastic molding on the rear hatch window door. If you open and lift up the rear hatch window.. on the right side (top-inward) of the plastic molding where it meets the glass at the rear section there is a seam in the molding that appears to join two separate pieces. When I put pressure on the seam it is very loose and rattles like the sounds I am hearing.

I haven't been able to verify this but when I do find a way to minimize the gap on the loose seam I'll see if the noise goes away.

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- 2005 X5 4.8is: LeMans Blue, Black/Blue Alcantara Leather Interior, Navi, Retractable cargo floor, Rear Side Impact Air Bags
- 2011 335i Sedan: Vermillion Red, Navi, Beige Leather Interior, Harmon Kardon Audio, Fully Loaded
- 2006 330xi Sedan: Titanium Silver, Navi, Dakota Leather, Fully Loaded
- 1987 Yamaha: Virago 700cc