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BMW M5 F90 (2018+) General Forums Mechanical Maintenance: Break-in | Oil & Fluids | Servicing | TSB | Recalls    Question: "Clunk" on shutting down: Is it the M Rear Axle Differential Lock?

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      09-30-2021, 12:28 PM   #1
delta
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Question: "Clunk" on shutting down: Is it the M Rear Axle Differential Lock?

Picked up a '21 LCI. First M5. I now have just over 2K miles. Enjoying the heck out of it.

But, as I've been getting used to the sounds and operating characteristics that any new ride presents, I've been noticing that when I shut off the ignition, I often get a one-time, audible "clunk" sound coming from the rear of the car. Not a loud nor metallic sound, but one that is definitely audible. Just a dull, summary clunk that I distinctly hear coming from the rear trunk/below trunk area just after pushing the engine start button to shut-off.

Perhaps as important a clue, the sound is accompanied by an abrupt shudder that I can feel through the driver's seat.

The noise and accompanying shudder does not occur every time. When I shut off the car on a level surface, it rarely occurs; but, I've noticed that if I shut off on an incline, or just after driving up an inclined surface to a level surface, and then shut off the ignition, I almost always, if not always, hear that "clunk" and hopefully benign, accompanying shudder.

--Is the "clunk" and accompanying shudder related to some kind of unloading of the M5's M rear axle differential lock?

--Is it some type of lock-up tension suddenly released from the differential at the time of ignition shut-off?

--Possibly an issue with the diffy's lock control unit?

I am not concerned at this point; Perhaps I should...

TIA!

Last edited by delta; 10-01-2021 at 12:47 AM.. Reason: For clarification
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      10-01-2021, 12:54 AM   #2
delta
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Moved thread to F90 M5 General Forum
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