Humming Noise: Constant Frequency Under Load

Hi!

I've already tried using the search function, but I haven't found anything.

'For some time now, I've been hearing a humming noise in my Lupo SDI when the engine is under more load. It's particularly noticeable when accelerating from low RPM and at low speeds. At highway speeds, it's masked by the road noise.'

'This noise doesn't occur when I give it gas while idling. It only happens under load. It also doesn't occur when I'm driving at a constant speed of 30 or 50.'

It sounds like an electromagnetic buzzer. The frequency is absolutely constant and completely independent of the motor speed and vehicle speed. It sounds like a relay is being switched off, which also causes a buzzing sound.

It doesn't seem to affect the driving characteristics or the engine power at all. It also doesn't go into a limp mode.

Interestingly, sometimes there's a brief humming sound for about 1 second when the engine is turned off.

Is that buzzing sound coming from a solenoid valve?

Thank you in advance.

You have a valve on the engine with a control unit (located under the hood, in front of the cylinder head, on the intake manifold). This component is making an extremely loud humming noise.
Try it out.