900 RPM is really fast, maybe try lowering the RPM to 500 or 550. A big problem with these threads is that everyone has a different idea of what is a vibration, mis(fire), buzz, hesitation, bog, noise etc. so that adds to the confusion and getting to the root of the issue.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)