[Mavallone]

I had a great drive this afternoon, but I noticed a clunking noise when down shifting towards the end of my 2hr drive. (6 spd Manual) Seems like it comes from the rear diff. And it occurs when I lift off of the clutch after a down shift with some engine braking. I searched the internet and I came across people who reported the same "thing", but no solid tech answer as to why it occurs. Is it a symptom of a mechanical problem? Definitely has me concerned

[m7ammed]

Originally Posted by Mavallone

I had a great drive this afternoon, but I noticed a clunking noise when down shifting towards the end of my 2hr drive. (6 spd Manual) Seems like it comes from the rear diff. And it occurs when I lift off of the clutch after a down shift with some engine braking. I searched the internet and I came across people who reported the same "thing", but no solid tech answer as to why it occurs. Is it a symptom of a mechanical problem? Definitely has me concerned

Why not take it to the dealer? the car should be under warranty still, no?

[Poochie]

It's probably the electronic locking diff, doing it's thing; it can emit noises..

If an idiot light didn't come on, then it's probably just fine and the nature of the beast..

[Mavallone]

Originally Posted by m7ammed

Why not take it to the dealer? the car should be under warranty still, no?

Yes. I have 194 miles. Just picked it up. The info I'm gathering is that it's normal but I am looking for some empirical data

[Mavallone]

Originally Posted by Poochie

It's probably the electronic locking diff, doing it's thing; it can be emit noises..

If an idiot light didn't come on, then it's probably just fine and the nature of the beast..

Poochie - I was hoping you would take the case! My concern is that it feels like slack in the drive train. Not sure that's a good thing. I did find this however in the owners manual, what BMW refers to as clicking, is more of a clunk that I feel.

[omasou]

M2 or M2C?

There were a few M2s early on that had a problem with the diff bracket bolt. Sorry, can't find a link.

My M2 would sometimes have a clunk when pulling out. I think it was slop before the diff engagement?

Here's a thread of various complaints.
https://f87.bimmerpost.com/forums/sh....php?t=1344418

Or like Poochie said could be the locking diff.

There was also a stop sale but those cars should have been fixed.

https://static.nhtsa.gov/odi/tsbs/20...47013-9999.pdf

[Mavallone]

Omasou - thank you for the feedback

M2C, just picked it up last week only a few hundred miles on the clock. Drove to the train this morning in efficient and all was quiet, 3rd to 2nd downshifts, even with engine braking caused no clunk. After work I will experiment with sport and Sport Plus.

[boss2k]

Are you sure its not a rock stuck in the calipers making a noise, i had similar issue in my old M3

[COChris]

This is normal from my experience and 13,000 miles in the M2C. Good to see BMW accepting more NVH for performance!

[omasou]

Originally Posted by boss2k

Are you sure its not a rock stuck in the calipers making a noise, i had similar issue in my old M3

I had both sounds on the M2 not M2C (knock on wood) the soda can crunch noise is very distinct.

Not sure about OP but the best way to describe my sound was...imagine a circle with a notch cut out of the interior...then imagine a rod keyed to fit the inner circle and notch...when you turn the rod the outer circle spins. In my case it sounded like the key had space around it and when I pulled out the rod rotated, slapped the inside of the notch making a clunk sound and then was quiet. This mostly happened from a dead stop but also sometimes when I lifted and reapplied the gas. Hope that makes sense. Might be the diff locking/unlocking but sound was intermittent.

Some talked about a bad diff bracket bolt, which for some reason there is only one, see Real OEM. I could imagine a similar sound would happen, if that bracket is not tight to the body. I think it. is part #2 or #7 https://www.realoem.com/bmw/enUS/sho...diagId=33_1838

[Poochie]

Originally Posted by Mavallone

Poochie - I was hoping you would take the case! My concern is that it feels like slack in the drive train. Not sure that's a good thing. I did find this however in the owners manual, what BMW refers to as clicking, is more of a clunk that I feel.

Thanx, it's nice to be appreciated

As I mention, the M LSDs, the crown-jewel of the model, tends to be noisy. That combined with the lack of sound insulation, gives the driver a more "raw" aural feedback.

Check out the video below, one of favorite automotive reviewers mention this at 6:10, as a point of contention:

[Al Bundy's Dodge]

My 2018 never clunks while driving. Only time I've heard it was occasionally shifting into first after having reversed into my parking spot. Previous RWD 6MT have made similar noises so I didn't really think anything of it

[Mavallone]

Originally Posted by Poochie

Thanx, it's nice to be appreciated

As I mention, the M LSDs, the crown-jewel of the model, tends to be noisy. That combined with the lack of sound insulation, gives the driver a more "raw" aural feedback.

Check out the video below, one of favorite automotive reviewers mention this at 6:10, as a point of contention:

I aprecicate the video, however that driver speaks of a whine... My noise is a distinct clunk... 50 Mph, strong breaking to enter a sharp right hander, downshift from 3rd to second, rev match, (thank you very much BMW) torque transfers to the rear diff. engine breaking starts to occur, then it happens: a distinct clunk sound coming from what seems to be the rear diff. like there was slack in the drive train that got taken up, and then the revs climb as I power out of the corner. No other noises. Car behaves perfectly. My dealer, who I have a great relationship with says its normal...

[Mavallone]

Originally Posted by omasou

I had both sounds on the M2 not M2C (knock on wood) the soda can crunch noise is very distinct.

Not sure about OP but the best way to describe my sound was...imagine a circle with a notch cut out of the interior...then imagine a rod keyed to fit the inner circle and notch...when you turn the rod the outer circle spins. In my case it sounded like the key had space around it and when I pulled out the rod rotated, slapped the inside of the notch making a clunk sound and then was quite. This mostly happened from a dead stop but also sometimes when I lifted and reapplied the gas. Hope that makes sense. Might be the diff locking/unlocking but sound was intermittent.

Some talked about a bad diff bracket bolt, which for some reason there is only one, see Real OEM. I could imagine a similar sound would happen, if that bracket is not tight to the body. I think it. is part #2 or #7 https://www.realoem.com/bmw/enUS/sho...diagId=33_1838

I like your complicated, but acurate analogy! Thats exactly what I envisioned. I am coming to the conclusion that its the plates in the dif smaking together when accepting torque loads

[Poochie]

Originally Posted by Mavallone

I aprecicate the video, however that driver speaks of a whine... My noise is a distinct clunk... 50 Mph, strong breaking to enter a sharp right hander, downshift from 3rd to second, rev match, (thank you very much BMW) torque transfers to the rear diff. engine breaking starts to occur, then it happens: a distinct clunk sound coming from what seems to be the rear diff. like there was slack in the drive train that got taken up, and then the revs climb as I power out of the corner. No other noises. Car behaves perfectly. My dealer, who I have a great relationship with says its normal...

I know yours is more of a knocking sound, just making it known that complains about various noises, in the diff area, are common and normal..

The diff is electronic, with a real-time temperature sensor, so if something would to go a-wire, the malfunction light would definitely illuminate.

However, its good that you got it documented with a dealer, should something does go bad in the future, which I doubt it will..

.

[AKRM2C]

Hi i think i might have the same problem. I have post it on youtube….

https://youtube.com/shorts/rd0PP7EQ9hc?feature=share

[HFW003]

Thank goodness it’s not the front diff!

[ioftendrive]

I had a great drive this afternoon, but I noticed a clunking noise when down shifting towards the end of my 2hr drive. (6 spd Manual) Seems like it comes from the rear diff. And it occurs when I lift off of the clutch after a down shift with some engine braking.

M car drivetrains are designed to be strong and stiff and the diff and gearbox has more backlash (slack in the gears) than a conventional drivetrain. Hence its a bit noisier and clunkier than a "normal" car.

[contented]

I get a clunk ocassionally, usually when on/off/on the throttle when pulling a hill or going around a sharp curve.

[Enabled]

Some clunks are normal since there is way less bushing insulation between it and the chassis. You will hear some of the noise due to backlash tolerances.

Many people's sensitivity can account for some variation, so it's difficult to separate that from normal and not.

[AKRM2C]

Sounds similar? Scanned it at the dealer with ISTA (3 times visit for the past 6 months) there appear to have no fault code related to the gearbox.

The only fault code is caused by my downpipes. And i am stock with no tune whatsoever.

Also posted a thread about this,

1 guy is like "get it checked asap it doesnt sound good"

1 guys is like "drivetrain sounds are normal, shouldnt worry too much"

Link to the thread
https://www.bimmerpost.com/forums/sh...php?p=27908734

[ESB]

Originally Posted by omasou

I had both sounds on the M2 not M2C (knock on wood) the soda can crunch noise is very distinct.

Not sure about OP but the best way to describe my sound was...imagine a circle with a notch cut out of the interior...then imagine a rod keyed to fit the inner circle and notch...when you turn the rod the outer circle spins. In my case it sounded like the key had space around it and when I pulled out the rod rotated, slapped the inside of the notch making a clunk sound and then was quiet. This mostly happened from a dead stop but also sometimes when I lifted and reapplied the gas. Hope that makes sense. Might be the diff locking/unlocking but sound was intermittent.

Some talked about a bad diff bracket bolt, which for some reason there is only one, see Real OEM. I could imagine a similar sound would happen, if that bracket is not tight to the body. I think it. is part #2 or #7 https://www.realoem.com/bmw/enUS/sho...diagId=33_1838

Super old thread I’m bumping but I wonder if this is what I’m hearing? Your description / image describes what I hear.

Sadly all previous videos are no longer working so I can’t compare. Here’s mine:

https://youtube.com/shorts/S3Dby5dJs...h2KmXFa2-RI1km

I’ve had my car for almost 4 years and > 30k miles and this only began happening yesterday after I took it into the dealer for a rear tire change and alignment.

I don’t remember it happening before but at the same time I’m not sure how a tire change could have triggered it especially if it really is related to rear diff….

I’m supposed to leave on a ~5000 mile road trip across the country next Friday 5/3 and ideally this will have stopped by then…

As you can see in the video it’s a bit of a small but audible clank that happens under initial load / brisk acceleration. Of course most frequently occurs from a stand-still but as shown in the video it can happen when you’re already moving and you apply sudden load / acceleration.