Engine Misfire: Humming Noise When Idling

hello

I have a Wendland tuning box installed in my Ibiza 6N with the AFN engine.

Since then, I've had a low-frequency humming noise (brrrgrrr) that I can particularly trigger in the following ways:
The car is stopped, in first gear, idling with the clutch pedal slightly depressed.
Press the clutch. The engine shakes for about 3 seconds and then runs normally again.
The sound is almost like a faulty bearing.
I don't understand why the noise fades away so quickly.
'Yesterday evening, the noise appeared on its own for the first time and didn't go away even when I tried to let the engine idle. However, if I put it under load or increase the RPM to 1200, the noise disappears.'

Could it be the dual-mass flywheel? Mine seems to be worn out. When changing loads, I can feel a 'thump' up to the fourth gear, which I believe is due to the dual-mass flywheel.

Please tell me that this isn't something really serious, like a main bearing or connecting rod bearing issue, or something like that!

Martin L. wrote:

The car is stopped, in first gear, idling with the clutch slightly depressed. Press the clutch. The engine shakes for about 3 seconds and then runs normally again.

Hi Martin,

The symptoms, to me, suggest a slightly over-revving idle, which is often caused by poorly designed components or incorrectly configured control units.

If you can eliminate the "problems" by temporarily disconnecting the box, I wouldn't worry about it any further .