Blubber Sounds: What Causes Them?

Hello!

I'm having a problem with my Golf 4, manufactured in August 2000, with a 1.9L engine and 85kW.

When I let the engine idle at approximately 2500 RPM, engage the clutch, and release the accelerator, I hear this strange gurgling noise!
Hard to describe!
However, this also applies during driving! But only when the clutch is engaged!
The noise is not audible from the outside, only inside.
Only occurs when the engine is running, not when it's idling: therefore, the clutch release bearing can be ruled out.

Thank you in advance. Best regards!

You have to admit that every answer to the question is pure speculation.
"Could you describe the sound in more detail? From which direction is it coming, and what does it sound like exactly? Does it only happen when the engine is cold, or also when it's warm? Have you made any changes to the vehicle since you started hearing these noises?"

Okay, one more thing: If it sounds like water is bubbling, try searching for "ZKD damage" (which refers to a damaged cylinder head gasket). It could be that there's air trapped in the indoor heat exchanger. Is the coolant level therefore too low?

For a 1.9 TDI AJM engine, I would immediately suspect a blown head gasket, as the bubbling seems to be coming from the heat exchanger. If you're still experiencing coolant loss at high RPMs, we're getting closer to identifying the problem.

Hi!
The noise is only audible when the engine is warm and also only when the clutch is engaged.
is being used!
There's a switch on the clutch, which in turn is monitored by the EDC (Electronic Diesel Control) system!
What is the purpose of the 'Schalöter' (likely a control switch) and what does it actually do? I don't have a cruise control.

The switch is used by the MSG (likely referring to a control module) to determine whether the clutch has been engaged. The MSG may also implement torque limiting. The switch is not only related to cruise control.