check the obvious first before you go nuts... check the tool kit under the trunk lid to make sure all is properly snug and clipped in their respective slots... also pull the left side panel and examine the amp and surrounding brackets to see if there is anything loose. you may also need to check the actual battery to see if it is loose...

could be anything...

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2012 X5 50i M-Sport
2014 X3 35i M-Sport