Brief grind noise on initial take off

[Ninjasteezify]

Hey guys, new to the forums and new to BMWs. Just picked up my long time dream car and first M a 2016 M4. Loving it and it is everything I've hoped it would be, but one thing that's perplexed me lately is a mild split second grind that occurs as i drive off and reach about 12mph. It'll make the sound once, and never again the rest of the drive. It also seems to only do it if the cars sat for a bit i.e. overnight. Sounds like a gear grind on a manual but I believe its coming from the rear.

I did not find anything conclusive from my research. Dont believe its rocks but have read speculation it could be the ABS self check noise, as it only happens at around 12mph and only once on initial take off and never again the rest of the drive. Anyone have this sound or know if its normal? if not normal any ideas what could cause it? Below is a video of the sound, it happens at 0:08 right after you hear the click of the doors locking.

I know these cars make lots of noise and maybe im just being overly paranoid. But I appreciate any help or insight.

[RoundelM3]

Most likely the M-Diff, normal operation.

[Ninjasteezify]

Good to hear it sounds normal. Coming from an Audi that was quiet and smooth this car is certainly an adjustment. It groans and whines and clunks but this grind noise is def the most alarming. Figured I ask tho as I would like to avoid going to the dealer if it’s common and there’s nothing wrong with the car.

[rborane]

I definitely don't hear any grinding on my car.. just the usual clunks and mechanical noises

[Ninjasteezify]

Yea Ive never noticed for the first month of having the car it was just a few days ago i started to hear it. Only does it taking off after a cold start, when it reaches 11-12mph and the rest of the drive is smooth and quiet. Which leads me to believe it’s some part of the operation of the car, since if something was loose or broken it should be doing it throughout the drive? But some say they don’t have the sound so that’s the real mystery I guess

[DanMpower]

Never heard that noise before in my car, but if you look at your tach, as soon as that noise is heard your warm-up redline drops 500 RPMs. I don't think that should happen...

[Ninjasteezify]

Interesting I hadn’t even noticed that..maybe the car detected a hangup in its normal cycle of operation thus prompting to limit the revs again? Hmm anything you guys would recommend I take a look at to try and self diagnose? I’ve fiddled with the handbrake to make sure that wasn’t hanging up, checked the wheels for stuck rocks, I’ve also looked under the car and didn’t see anything out of place but I’m not a mechanic so something broken could have been staring at me right in the face...

[TrauCon]

Same on mine, that exact noise!
Lol at the exact same speed and right after it locks the door.
I am not worry about it.

[Ninjasteezify]

I knew I wasnt alone! I have read a few reports of the same short grind noise happening around 12-15mph many thought it was the ABS self check making noise. Either way I am bringing the car to my local BMW specialist shop to have it checked over and make sure nothings out of wack. Will report back to confirm whether this is a common quirk or something is acting up.

[TrauCon]

Originally Posted by Ninjasteezify

I knew I wasnt alone! I have read a few reports of the same short grind noise happening around 12-15mph, as stated many thought it could have been the ABS self check making noise. Either way I am bringing the car to my local BMW specialist shop to have it checked over and make sure nothings out of wack. Will report back to confirm whether this is a common quirk or something is acting up.

Let me know what they say. Thanks in advance.
My thought is something programmed into the car to check/do something at that speed. If something was wrong hardware wise, I would expect the same noise happens at other times. Car is perfectly fine. You have the same year as me too, so maybe just us. Lol.

[Ninjasteezify]

That's what I was thinking too, the fact it only happens one time everytime at that speed makes me believe its some normal function of the car making noise. But also some people reporting they dont get the noise def has me intrigued. Will make sure to update later this week when I find out more from my shop!

[Ninjasteezify]

Update got the car back yesterday and noise is still there. The shop did not find anything that is obvious to the noise so they performed a transmission adaptation reset and diff fluid change. Noise does seem to be more subtle now or maybe its just in my head. My mechanic also noticed some play (a few mm of movement) in one of the drive axles, said that may be part of the issue. Is it supposed to move like that?

[TrauCon]

Originally Posted by Ninjasteezify

Update got the car back yesterday and noise is still there. The shop did not find anything that is obvious to the noise so they performed a transmission adaptation reset and diff fluid change. Noise does seem to be more subtle now or maybe its just in my head. My mechanic also noticed some play (a few mm of movement) in one of the drive axles, said that may be part of the issue. Is it supposed to move like that?

If it is that moment then it would happen more often. This just when we ride out on the first trip of the day, happens 1 time, at the exact speed.
Also someone correct me if I am wrong but a tiny bit of movement there is okay because of the bushing.

[Ninjasteezify]

I think you’re right i did read that E92 M3’s have that same movement so it should be normal for F80/F82 as well. Interesting find though I took a lavalier mic I had and wired it under the car to see if I can pinpoint the origin of the noise. Initially pointing at the diff, caught the noise but sounded faint and distant. Out of curiosity I put it close to the passenger rear wheel and pointed it right at the brakes and sound was loud and more prominent. May or may not mean anything I’m definitely gonna try a couple more spots before jumping to conclusions. Was ready to give up and run with it but quarantine life’s got me restless

[Crawford0719]

Originally Posted by RoundelM3

Most likely the M-Diff, normal operation.

I have a 2020 ZCP that makes a clunk taking off in first gear from the back. 1400 miles on the car. This seems a bit much though? Kind of hard to tell from the video.

[RoundelM3]

Originally Posted by Crawford0719

I have a 2020 ZCP that makes a clunk taking off in first gear from the back. 1400 miles on the car. This seems a bit much though? Kind of hard to tell from the video.

The "clunk" and the "grind" symptoms are different; my diff made the "grind" noise when cornering sometimes until I had it coded to GTS level. The "clunk" on takeoff is something entirely different, but it may depend on what mode you have the trans in.

[Crawford0719]

Originally Posted by RoundelM3

The "clunk" and the "grind" symptoms are different; my diff made the "grind" noise when cornering sometimes until I had it coded to GTS level. The "clunk" on takeoff is something entirely different, but it may depend on what mode you have the trans in.

My symptom seems to occur on sports plus engine with the trans in the most aggressive state. The general gear engaging I get. My issue goes like this. Mind you I am in manual mode and car is warm and I am not pushing it at all. Very smooth take off.

I roll out on first gently, at about 5-15mph there is a click/light clunk from the back. Then goes away.

[RoundelM3]

Originally Posted by Crawford0719

My symptom seems to occur on sports plus engine with the trans in the most aggressive state. The general gear engaging I get. My issue goes like this. Mind you I am in manual mode and car is warm and I am not pushing it at all. Very smooth take off.

I roll out on first gently, at about 5-15mph there is a click/light clunk from the back. Then goes away.

It might just be the diff "locking up" (normal operation), as I get the same thing after parking my car, maybe 30 seconds after the engine is shut down. As new as your car is, you might just have the dealership check it to be sure there isn't something amiss.

[Ninjasteezify]

Just wanted to give an update with some interesting findings as I've had some extra time the last week or so to revisit this. Done a few recordings underneath the car and none sounded particularly clear. Recordings of the diff were quiet. No sounds coming from the diff. The sound seems more prominent from inside the cabin, which gave me the idea it may not be coming from outside the car at all, rather the inside. Just for sh1ts I took a recording of the fuel pump directly underneath the back seat. With the backseat removed the sound is the closest and loudest I've heard it so far. Sounds like it may be the fuel pump priming or the lines filling up/pressurizing? You can't see much in the video with my phone pressed up against the seat cover, but you can definitely hear it, 00:19 right after the car shifts. Again, not 100% conclusive but for now I'm gonna assume that's what it is unless someone has other ideas what it could be.