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      10-19-2012, 07:35 PM   #13
MilehighM3
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Drives: E90 M3
Join Date: May 2011
Location: Colorado Springs

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It is normal. It's a characteristic of the variable M differential lock. You can also hear it in the parking lot rolling in first gear at idle and disengaging the clutch. The rattle at idle when hot is due to the use of a twin disc clutch. It's actually pretty quiet compared to the average aftermarket twin disc set up.