[Merlino31]

Hi guys! I have an annoying problem with my 320d 6mt f31 07/2014: there is a rattle very similar to the engine cover rattle or airbox rattle coming from engine bay but I'm unable to locate! I changed induct of airbox, pads, angine cover pads (also tried to remove it) but the rattle still there! You can hear when the car is idling or rpm drops at the min. If you remove the airbox and put it back at the first time it seems solved but after a short trip (5km?) it comes back! Any idea? I tried to turn off AC but nothing changed and you can also hear the rattle when passing on bumps at low rpms or press gas pedal at about 1200rpm or less.

[n00bkiller944]

You sure it isn't timing chain noise from a stretched chain?

[mapyn]

there was a thread identifying a similar rattle from the washer bottle within the front wheelarch. apparently there's supposed to be some foam in there to stop it. i suspect mine has this issue but haven't asked anyone to trace it yet

[Merlino31]

Timing chain checked and it's fine, washing tank the same.
Here is a video of the noise: sometimes is there, sometimes not. If you press the gas just over the minimum it starts and it doesn't change if the clutch is depressed with 1st gear in or in neutral without the clutch down.
Today I went to the dealer asking about that and he said, after testing the car, that could be everything for example a spring of the flywheel that get stuck sometimes but it could be strange because should be always there.
https://youtube.com/shorts/eeDGPx0LcNc

[Merlino31]

I found this video which is exactly the same rattle I hear https://player.vimeo.com/video/70102...E%3C/iframe%3E

[Eddamoo]

Both 2l BMW diesels i've owned (a 120d and an X4 20d) have suffered a similar rattle that came from the AC pipes where they enter the cabin. On the X4 i resorted to having to stuff an old blanket around the pipes where they meet the bulkhead on both sides. Worth a shot!

[Merlino31]

Is possible to access it from inside the car?

[Eddamoo]

Yes they go to the heater matrix which is behind the Glovebox. The pipes are aluminium and run from the AC radiator to the bulkhead - Its easier to get to them in the engine bay. Just get a friend to hold onto the pipes while you can hear the noise; just holding onto them should change or mute the noise to see if its that.

[Merlino31]

When I replaced the muffler they added a bracket and the rubber now is broken and it is ratteling

[capt_slow]

The symptoms appear similar to what I just found on my F31's airbox. While engine is running at idle, apply press down on various parts of the airbox or other contact points in the bay to see if the rattle goes away.

In my case, I found it my accidentally leaning on the (US) passenger side of the box during an inspection and the rattle went away. Turns out the airbox was not properly seated into the intake duct attached to the front bumper. The airbox mounting points will still engage, but you will see a small gap between the air duct and the airbox. Reseating the airbox and ensuring it makes a clean seal with the duct made the rattle go away.

The duct is Item 9 in this diagram:

[Merlino31]

Problem solved!

The problem was very difficult to find online because the 320d has only exhaust mounts in the back near the muffler but on mine, when I changed the muffler with a 335i style they mounted a support just back the gearbox.
The rubber support was broken and at idle it vibrates on metal bars. My mechanic zip tied the rubber and the rattle disappeared! Yesterday Inreplaced the rubber and now is silent.