Help diagnosing drivetrain rattle

[F1FL]

Hi everyone,

After years with the M3 I’ve had a few issues pop up within the last 10k miles. Right now I’m experiencing a strange “rattle” noise coming from what seems like the transmission tunnel. This is not an interior rattle but definitely drivetrain related.

Including a video, I am cruising in 4th gear and then slow down without shifting. This noise seems to happen only in lower gears right before shifting down a gear. Seems to happen more when engine is cold, but this video it is warm. Any thoughts? No codes thrown during these occurrences.

One thing to mention is I changed my rear exhaust section back to stock about 1k miles ago, but this is happening only recently. Re checked everything and connections are fine/tight.

E92 M3 drivetrain rattle

[Redd]

Check your exhaust heat shields, especially the ones around the drive shaft.

[DrFerry]

I agree with Redd - It's an exhaust heat shield resonating at a certain critical speed. I hear it briefly in the middle of the video you posted.

[F1FL]

Originally Posted by Redd

Check your exhaust heat shields, especially the ones around the drive shaft.

Originally Posted by DrFerry

I agree with Redd - It's an exhaust heat shield resonating at a certain critical speed. I hear it briefly in the middle of the video you posted.

Are either of you guys familiar with what exactly would be loose? Are there bolts that secure the heat shields to the body? I will try to get under there later this afternoon.

[Redd]

Yes there are screws/clips. The shields could also be bent and vibrating against other shields - or against the driveshaft - at specific rpms. The driveshaft might be trickier to check as you may need to drop the exhaust. You just need to get under the car and check everything.

[DrFerry]

Originally Posted by F1FL

Are either of you guys familiar with what exactly would be loose? Are there bolts that secure the heat shields to the body? I will try to get under there later this afternoon.

Take a look at these images to see ALL of the heat shields the E9X M3s have! Try to determine the approximate area the rattle is coming from then check for loose fasteners and screws. The image with the red box is from Redd advising me where to look for the source of a dash rattle I have that is most like caused by a heat shield. In your case; see the BMW part drawing for all the heat shields possibly involved towards the back half (rear) of the exhaust.
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[Redd]

Yeah and note that many shields overlap each other. If one is a bit bent it may provide a gap which will rattle under specific rpm / vibration frequencies.

What u should do:

1. Bang on the exhaust with my fist throughout it's length to see if it is contacting the heatshields in any way, or if there are any broken brackets.

2. Check for missing screws - look for holes that don't have screws/clips on the heatshields and the black underbody side panels.

3. Tighten all screws.

4. Check the heatshields between the exhaust and the driveshaft. The ds is literally just behind the heatshields and there is nothing stopping the aluminum shield from contacting the rotating ds. Especially at the ds couplings and center u-joint which is larger than the rest of the ds. Make sure that's not contacting the heatshields in anyway.

Many times just 1-2mm can make a difference so check thoroughly.

[roastbeef]

gotta get under there and poke around. thats right about where the guibo off the dct would be as well, but i think that would be a more pronounced noise.