[thealbert]

Hey guys. I picked up a G20 M340 xDrive just last week for the dealer. It's brandnew. On the way home from the dealer, I noticed there was a thud noise coming from the rear when the car is coming to a stop. Checked around the back trunk and nothing was there. It generally happens when the car is slowing down to a gradual stop and i'm on the brakes during almost any situation, like stop and go traffic or coming to a red light. It makes the noise only once right before the car comes to a halt. It kind of sounds like something is moving around back there and its not a metallic sound. Anyone else encounter the same problem?

**UPDATE**

Took the car to the dealer. Kudos to the dealer at least, they couldn't hear the noise at first during the test drive but they kept at it until they did. They heard the noise and at first thought it was the brakes but that was quickly ruled out when they heard the noise even then the brakes are not being applied. The tech guy tried reversing and we heard the noise as well. The sound came out the moment the car started to move from standstill in reverse. So from the looks of it, they think its a drivetrain issue and likely something to do with the differential. They're checking the diff fluid levels at this very moment in time. Will update you guys on more once I get more info.

[wtwo3]

Did you check under the trunk cover where a spare tire normally would be to see if there are any loose parts (i.e. toolkit)?

If it's easily replicated and you can't find anything loose, I would take it in to the dealer.

[A6bullet]

Hmm, well this car comes with the M diff, or a version of it. Might be that notorious clunk that M cars have.

[Delta5]

FWIW, my RWD M340i doesn't do this.

[golferboy2312]

I have an M340i xDrive with almost all options. No sounds from the back.

[Top Gon]

The diff in my M2 used to make a thud but only when making a sharp turn and the inside wheel is in the air

[Transfer]

Spare tire or no spare tire?

[thealbert]

Took the car to the dealer. Kudos to the dealer at least, they couldn't hear the noise at first during the test drive but they kept at it until they did. They heard the noise and at first thought it was the brakes but that was quickly ruled out when they heard the noise even then the brakes are not being applied. The tech guy tried reversing and we heard the noise as well. The sound came out the moment the car started to move from standstill in reverse. So from the looks of it, they think its a drivetrain issue and likely something to do with the differential. They're checking the diff fluid levels at this very moment in time. Will update you guys on more once I get more info.

[thealbert]

Originally Posted by Transfer

Spare tire or no spare tire?

there is no spare tire in the car. relies on run flats.

[thealbert]

Originally Posted by golferboy2312

I have an M340i xDrive with almost all options. No sounds from the back.

Thanks for the info. Hopefully its not a major issue on my end.

[thealbert]

Originally Posted by A6bullet

Hmm, well this car comes with the M diff, or a version of it. Might be that notorious clunk that M cars have.

That is possible. I didn't realize the diff on the M340i is a M one. Silly me for not connecting the dots. Any idea specifically what kind of diff it is? Keep in mind, my unit is an xDrive.

[thealbert]

Originally Posted by Delta5

FWIW, my RWD M340i doesn't do this.

Thanks for the info! Looks like mine clearly has something up. Definitely not part of the normal operation of the car.

[A6bullet]

Originally Posted by thealbert

That is possible. I didn't realize the diff on the M340i is a M one. Silly me for not connecting the dots. Any idea specifically what kind of diff it is? Keep in mind, my unit is an xDrive.

Hmm as far as I know x Drive or not you'll have the Diff. From another post in the forums, which I cant recall right now, a guy was using eSYS I think? to look up stuff in his car, turns out the info in the Diff electronics mathced that of the F87 M2, which confirmed it was an M unit of extremely similar. Ill do some looking around so I can point you in the right direction.

Found it! https://g20.bimmerpost.com/forums/sh...48&postcount=4

[thealbert]

Originally Posted by A6bullet

Hmm as far as I know x Drive or not you'll have the Diff. From another post in the forums, which I cant recall right now, a guy was using eSYS I think? to look up stuff in his car, turns out the info in the Diff electronics mathced that of the F87 M2, which confirmed it was an M unit of extremely similar. Ill do some looking around so I can point you in the right direction.

Found it! https://g20.bimmerpost.com/forums/sh...48&postcount=4

Thanks so much for the info! I'll drive the M2 and see if the sounds are similar.

[thealbert]

Update:

Got the car back from the dealer. Sound is still there (why am I not surprised). The dealer said they tightened up some bolts and check the diff fluid levels and all were ok. They suggest for me to drive the car around a bit more and then come back next week for a diff fluid change and a running in check. Not quite sure what they do in a "running-in" check. Well, looks like I'm out of luck for now and will just have to live with it. The tech guys at BMW did say it was safe to still drive. Let's hope so. At least there's a record of me complaining to my dealer about this issue coming up this early in the car's lifespan. Let's just see how the car settles after the break-in is done.

[jonlimawan]

Albert did you ever get this resolved?

[thealbert]

Originally Posted by jonlimawan

Albert did you ever get this resolved?

I took the car to the dealer and they physically checked the whole rear drivetrain and driveshaft assembly of the car. They didn't find anything lose. They also reprogrammed the car and its transmission settings. They said there was an update since my car was produced so I was hopeful the problem would have been solved with a software update. Sadly, no immediate change after this dealership trip.

Took the car back for a second trip a couple days after and the dealer escalated the issue and even the BMW mastertech had a look at the car. They came to the conclusion to run the car a bit longer and finish my break-in period first. If the "thud"/"dung" issue gets worst or is still present after the break-in period, then I should bring the car back and they plan to escalate it to BMW Germany itself. I wonder why they didn't even do that in the first place. But anyway, ok, they were really nice and respectful about the whole situation so I figured they were just following their set procedures.

2.5k km later and I still hear the thud/dung noise but it is a lot more faint now. Sometimes I don't hear it at all anymore, versus when the car was new, it was making the thud/dung every time the car comes to a stop or when slowly accelerating.

I've noticed that the more I drive the car, the less it got. Maybe the dealer was right and the car just needed to be run in a bit more. The car's not really used much yet, thanks for covid-19 but I'm still observing the issue as I get more mileage on it.

I hope this helps!

[Voodoo_G80]

What’s up man, I’m having the same issue. It’s a loud thud sound when accelerating from a standstill, accelerating in reverse, or when I just punch it on the highway. I’ve had this sound for a few months and it’s getting worse. Haven’t taken it in yet but I’m pretty sure the rear differential needs to be replaced. I will be taking my car in for service after this holiday. I don’t feel like it’s safe to keep driving with this. You’re not alone haha.

[thealbert]

Originally Posted by Orange_m340i

What’s up man, I’m having the same issue. It’s a loud thud sound when accelerating from a standstill, accelerating in reverse, or when I just punch it on the highway. I’ve had this sound for a few months and it’s getting worse. Haven’t taken it in yet but I’m pretty sure the rear differential needs to be replaced. I will be taking my car in for service after this holiday. I don’t feel like it’s safe to keep driving with this. You’re not alone haha.

That's interesting since mine seemed to have gotten better over time. What's the current mileage on your car? Did you feel and hear the thud sound when the car was brandnew?