Not sure if links to other forums are welcome here or not.. so just copy-pasting it
Quote:
"I'm with BMW of North America, LLC. The M3 is a refined version BMW's race cars. It is designed to provide optimum power and performance in a street legal package.
In order to transmit engine torque to the rear wheels instantaneously, without any time lag, the whole M3 power train was designed with maximum torsional rigidity. To achieve this maximum torsional rigidity, the flywheel mass and its damping capability has been reduced to a minimum.
As a result, during an abrupt torque transfer (e.g. 1st to 2nd gearshift at low engine speeds) the driver can receive an acoustic feedback, which can be interpreted as a "clunking or rattling" noise.
The acoustic feedback characteristic is not a symptom of a failure, and does not compromise long-term reliability of drivetrain components (clutch, transmission, differential), nor does it adversely affect performance of the vehicle.
If you have any questions, you can phone us at 800-831-1117. "
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My take is that the clunking noise comes from the DMF when its springs gets compressed / decompressed suddenly.