Whining Noise Front Right, Golf 4 ALH

Hello everyone,
Recently, I noticed that my Golf 4 ALH engine makes hissing sounds during the warm-up phase.
The noise can only be heard when the radio is turned off and with very attentive listening. It seems to be coming from the area in front of the dashboard on the passenger side, although localizing sounds is always very difficult and far from clear. Of course, the fan was turned off .
Certainly, this noise only occurs when the engine is cold. Once the engine reaches operating temperature, it disappears. The air conditioning compressor/evaporator can also be ruled out, as it is not present .
It also doesn't appear to be a leak in the turbocharger system, as the noise intensity is practically independent of engine load and is particularly noticeable at idle, where the boost pressure is nearly zero.

Could it be due to residual air in the cooling system? Recently, a badger gnawed through the lower radiator hose. The system was refilled after that. Is it possible that the heating heat exchanger still contains residual air and is making hissing noises during the warm-up phase?

Ich habe sonst keine Idee mehr was es sein könnte. Who has advice?

Regards,
Alex.

If you say it's coming from the direction of the dashboard/passenger side, then I remember a discussion we had here about something similar: There was a piece of foam padding that was either improperly installed or had shifted out of place, underneath the dashboard/glove compartment. Could the hissing sound possibly be a vibration that only occurs when the engine is cold, because the engine itself is vibrating more strongly at that time?

I don't believe the story about the cooling system; even if there were air in it, why would it hiss? It's not leaking anywhere. It's just accumulating at the highest point.

Holger247 wrote:

There was a piece of foam padding that was either poorly fitted or had shifted out of place, underneath the dashboard / glove compartment.

That would be here:
/viewtopic.php?t=5034&highlight=klappern

I don't believe that; it made a very loud clacking sound. That's not even remotely like a hiss... But I'm open to being convinced.

hello

It could also be the beginning of a problem with the head gasket. The head gasket is damaged in one place, and exhaust gases are being forced into the cooling system, which is then under higher pressure. The gurgling sound is coming from the heat exchanger, which is located under the glove compartment in the dashboard. The gurgling can also occur during cornering, but it's not as noticeable then as it is when the engine is cold.

Best regards.

hb2000

"Of course, if it were a ZKD (cylinder head gasket) issue, that would be quite something! When the engine is cold, I should be able to see bubbles or hear loud hissing noises by opening the expansion tank cap, right?"
Question: Why would the noise only occur when the engine is cold, if it's a head gasket issue? The chamber pressures (which I can influence through my driving style) are lower when the engine is cold compared to when it's at operating temperature. In my opinion, this contradicts that theory!

Regards,
Alex.

Hello,
"Try checking the area near the diesel filter, specifically the thermostatic valve, with the hood open. At least, that's where I found it on my car. It's not noticeable in the summer due to the high temperatures, but now that it's getting cooler, the valve is making that noise again until the return diesel reaches its operating temperature."
I think that's also the case, and that no "ZKD" (or "ZKD-fear") comes into play .

Best regards,
Andreas

Hello everyone!

Quote:

Point the ears while the hood is open, towards the diesel filter, specifically the thermostatic valve. That's at least how it was for me, or for my Alh

.

That sounds reasonable and plausible, and it also aligns with my sound localization from inside the room.

Does anyone know at what fuel temperature the valve switches? It hasn't been quite that cold in the past few days. The outside temperature must have been around 17-19°C when I first noticed the noise.

Regards,
Alex.