So I have a bit of an issue. Based on what I have read around here on the forums and watching YouTube videos, I don't think it is turbo bearings, but I am not sure. I've replaced the DV to no avail. I am not sure where to do from here.

The best I can describe it, is its an intermittent choppy whistling noise. It does not happen every single time I accelerate hard (happens about 70% of the time), nor does it do it the entire power band of accelerating. It does not seem to matter if the engine is cold or warm. I have not noticed any extra smoke from the exhaust. I have linked a video that I took from inside the cabin and you can hear it. (It doesn't sound like any of the other videos I've seen that the turbos are 'whistling')

Below is the timeline/details of the issue and car.

2009 A4 Quattro - 64k Miles (Purchased about a month ago-- Totally stock, no noises)
I live at an altitude of 4,300 feet
Installed an APR Carbonio intake
Did not notice this odd intermittent choppy whistling noise after installing the intake
3-4 days after Intake install, got an APR Stage 1 tune done
Either that same day after leaving the shop, or the next day, I started to notice this odd noise while accelerating hard.
Can usually only hear the noise from about 2,000 - 3,800-ish rpm.
I do not hear the noise under normal/light driving-- Only when accelerating harder
Does not make the noise if sitting still and raising the revs
Sound immediately goes away after releasing the throttle
Installed a GFB DV+ Diverter Valve -- sound still there. No change. (Stock DV was the newer style, not the diaphragm style)
No codes from the VAGCOM
I took some logs of the requested boost/charge vs actual log from vagcom-- I am no pro at reading this, but it seems like I am not losing any boost. (At least the time that I was logging) VAGCOM RUN 1 VAGCOM RUN 2
However, sometimes I do think I am losing boost because I can see my needle slightly bounce as I am accelerating while the noise can be heard. However, this is not very often that I notice this.
The sound can still be heard if I change the APR program to 'stock', but it is not nearly as loud/often as running the 91 octane program.

I took it into the shop that did the APR tune to take a look. For $125, they did an initial diagnoses and checked a few different things, including removing the intercooler pipe and found some oil in it. Now they want to charge another $350 to take the downpipe off and take a look at the turbo to find out if there is any give/play in the shaft and to look at the bearings.

Is it possible that this is just the sound of air rushing in through the turbo or exhaust and its completely normal? The reason why I don't think its normal is that I can run the 'stock' program and I can still hear it, and this only reared its head after getting the stage 1 tune done.

Any thoughts anyone? Quite the head scratcher-- but I am no mechanic by any means.

The first part of the video is hitting it hard in automatic. Second part of video I am in 3rd gear hitting it hard, and then letting it rev down. You can hear it 2-3 seconds, 5 seconds, 10-11 sec, and 18-19 sec.

 

I wished I could help but I have almost zero experience with the turbo flavored engines. However, I don't think turbo engines that have been "modded" are going to be all that quiet when you get on it.

 

Did you ever figure out what this was? I have an 09 avant that makes the same noise. Mine isn't as loud but it is definitely the same noise. I can't get it on video because you can only hear it clearly when the window is down, and then if I video it, all you hear is motor and wind. Lol

 

Since your Avant is doing it, let me suggest that it could be the PCV valve. Sometimes they can develop a tear in the diaphragm that will cause a whistling flutter sound when you accelerate. My A8 was doing it a while back. I had a spare PCV valve and swapped it out. Noise went away. I haven't taken the fluttering PCV valve apart yet to see what it was..

 

Resurrecting this thread.
I also had the turbocharger installed though OEM after the old one was no longer boosting and once out of shop I am getting exactly the same whistle. I had that in another shop who has suggested to replace turbo again and I have done that myself now and choppy whistle is still there during boost. Obviously this is not a turbo issue and so called Audi specialist in one of the local shops sent me to the rabbit hole.
Long story short...has anyone resolved it by replacing the PCV?

You Tube

 

Replaced the oil separator and whistle is still there.