[VIDEO] 118d - Fluctuating engine noise, but stable RPM, any idea?

[quentinvidal]

Hi everyone,
I just bought a 118d E87 2010 with the infamous N47 engine, and it is making that weird fluctuating noise, which you can find in the video: https://www.youtube.com/watch?v=1ibwIrlq5aY

It makes this noise mainly when the engine is hot and idling (Pretty sure I can hear it too when driving). However, the RPMs remain stable, which is weird.

The car also jerks in cruising mode, rarely, but when it does, it is very obvious, as if there was a misfire. Then If I accelerate, it will go away, till I use the cruising mode again.

I also realised that, when parked, the engine noise fluctuates when I brake, and even fluctuates when I use the blinker! It will follow the same frequency as the blinker... How is that possible? It will be louder when I release the brake pedal and quieter when I press the brake pedal, as if, by doing so, I would tighten something loose and prevent this "something" to shake. Also I sometimes have the orange battery light displayed on the dashboard, once I off the engine, so I suppose it has something to do with the alternator.

Probably having several problems at once...


I am going to change the timing chain + guides, and the clutch + flywheel soon, (because N47 yes), but I don't think the noise(s) is/are related to any of those parts.

Any ideas???