Maybe an engine misfire ? No codes ? I would look for that thread were I think someone else went through this, maybe even with the Corteco mounts which FCP claims to be OE. I think the trans mount can be an issue too.

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