Turbo Whistle A6: Strange Noise & Causes

Hello everyone,

"In my A6, manufactured in August 2004, with engine code BDG (Euro 4 with throttle valve), I've recently noticed the following:"
When I'm under load, meaning when the turbocharger is producing high boost pressure, if I release the accelerator or shift gears, it releases the boost pressure like a blow-off valve – at least, that's what it sounds like. The noise isn't very loud; you can only hear it when it's completely silent. I would also say that the higher the boost pressure, the louder the noise.
Since I installed an LDA on my previous diesel engine, I simply claim to be able to judge when high boost pressure should be applied .
It sounds like a kind of hissing or grinding noise. The noise is not noticeable when the engine is idling, i.e., without any load.
I also considered whether it could be coming from the transmission (TT), but if that were the case, it would also occur when the turbo isn't under load.
By the way, there is no error entry.
The car received an ODB tuning approximately 2000 km ago, and shortly after that, the noise could no longer be detected.
Does anyone have any suggestions as to what might be causing this?
Thank you very much for your answers!

I had already checked the AGR (presumably referring to a specific system or process) for compliance with regulations, and everything was in order.

Hello Sunseeker.

With an LDA (Laser Detection and Ranging system), one could immediately detect high LD (Laser Detection) signatures.
But I think that with the chip tuning, the pressure will likely be higher than the standard setting.

However, a hissing sound is more likely to indicate a leak in the charge air cooler system.
Perhaps you could remove the underbody protection and check if you find any oily spots on the hoses of the hydraulic system.
Although it seems a little excessive, it's probably normal because the clamps probably aren't as tight as they should be.

Check your LLK (low loader trailer) and inspect it for any damage. If you're already looking at it, also check if it's clean .

I see it this way:

"The chip likely increased your boost pressure slightly. When you let off the gas, you'll always hear that kind of hissing sound, as you described. Because the boost pressure is higher, the noise is also louder, but you just didn't hear it before. I would say that everything is probably fine. If you were to hear the noise under load, it could indicate a leak, but not when you're letting off the gas."

Thank you in advance for your answers. I haven't found any leaks.
And the post by mserge actually makes me feel a little more reassured .

I hear that sound too, and I like it.
It happens when I'm between 1700 and 2000 RPM, when I'm giving it full throttle and quickly release the accelerator while simultaneously pressing the clutch.
This noise is further amplified in my case by the sports air filter and the modified exhaust system.

As "mserge" already mentioned, it comes from the turbo. It's a kind of after-effect of the turbine or a braking mechanism.

It reminds me a bit of a Scania with a V8 engine and a modified exhaust system.

http://de.youtube.com/watch?v=UKzrknnUXb8&feature=related

http://de.youtube.com/watch?v=KTu6o7i4h50&feature=related

Pay attention to the howling!
At that moment, he releases the accelerator, quickly presses the clutch, and shifts gears.
Due to the larger turbocharger (with greater inertia!) in the truck, what was a "whine" (from the car) becomes a "roar"!

The second one is an automatic, with a shorter, higher-pitched whine.

Technical data for the Scania 144/530:
V8 engine, 4 valves per cylinder, 14 liters of displacement.
Power: 530 hp at 1900 rpm.
Torque: 2500 Nm at 1100 rpm to 1300 rpm.
Electrically controlled in-line injection pump.
Idle speed: approximately 550 RPM.
12+1 speed manual transmission with 2 reverse gears, or an automated option (including clutch, for starting, which automatically shifts gears).

Hello!

germa wrote:

I also have that sound, and I like it. It occurs for me between 1700 RPM and 2000 RPM when I give it full throttle and quickly release the accelerator pedal within that RPM range, while simultaneously pressing the clutch.

I can absolutely agree with germa's statement! I experience the same thing under the same circumstances! However, I must mention that in my vehicle, neither a chip nor a sports air filter is installed, nor has the EGR system been modified. The theory that it's a kind of afterglow or braking of the turbine is what I find most plausible.

Best regards,
Stefan

I'm also experiencing this noise with my ARL engine and VNT-20 turbocharger, although the volume is different. I've never noticed it as clearly as I do now.

I'm really curious now about how it actually happens. What happens when you switch from gas to electric, and in what order?

Hello, fellow diesel enthusiasts.
I recognize that sound too, but not from cars, but from trucks and tractors.
My Fiat tractor, manufactured in 1973 and fitted with an aftermarket turbocharger, also makes that noise.
If I quickly release the throttle to shift gears while under full load, just before the engine starts to bog down, it makes a loud whining noise.
I suspect that the elimination of fuel injection will affect the exhaust gas temperature, and consequently...
The exhaust volume drops sharply. The exhaust turbine needs some time (approximately 1 second) to adjust its speed.
to come down, and 'sucks' during that time.

Best regards, Chrigu.