Strange Noise (Turbo or Transmission?)

Hi,
We treated ourselves to a Volvo V70 D5 from the 2004 model year, and now, with a mileage of almost 250,000 km, I'm doing some things to take good care of it.
It has been consistently maintained by Volvo and is in good condition for its age.
Okay, first, remove and clean the intake manifold cover. Then, remove the EGR cooler and do the same. The carbon buildup in the pipe from the EGR was between 1-2 cm thick :-O.
I also noticed that there's excessive pressure in the engine, which is why I also want to replace the oil separator and the associated piping.

Now, I'm concerned about this strange noise that I can't quite understand, and that's why I'm asking you, since you were able to give me good advice before .
It's a kind of hissing or grinding sound (sorry, I don't know how else to describe it), and it only happens when a gear is engaged. It's more noticeable when accelerating, but it can also be heard with a gear engaged even when you're not accelerating.
As soon as I take my foot off the accelerator pedal while driving, the noise is less noticeable than when accelerating, but it's still present. However, when I disengage the clutch and let the car roll, the noise is no longer audible.
It's also not there when the engine is idling.

Currently, I suspect it might be a vacuum leak, as I also feel that the car is not responding to the accelerator as quickly as it should, or not accelerating as much as it could.
That's why I ordered a vacuum tester. Could it really be due to that?
Furthermore, I'm not ruling out the turbocharger, or perhaps the transmission; am I on the wrong track here?

I would really appreciate your opinion.
Best regards, Albert.

Hi,

If you record a video with your phone and upload it here (select file + etc.), we can also do something with the audio.

Have you already checked the charge air cooler for leaks? The more you accelerate, the more boost pressure is built up, and the louder the hissing will be if there are any leaks.
There are already many discussions and articles about leaks in the charge air cooler system; see the "Related Topics" section at the bottom and use the search function for more information.

Inspection of the charge air cooler system:
Okay, I understand. Please provide the German text you want me to translate into English. I will only provide the translation.

Best regards, Rainer.

Hi Rainer,
Thank you, good idea. I will reassemble the car and do the video about it .
Yes, that was my assumption as well, but I couldn't find any leaks. :-{
I will still check the link right away.

I tried recording it with my phone. It's not easy to recognize, but it's still my best recording of all the other attempts .

Sounds like whistling / hissing from a leak in the intercooler piping.

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