Identify these moans

[okhan]

Since upgrading my 2005 A4 1.8TQM with a K04-15 and a Unitronic tune I've been getting a moaning sound that starts around 2400 rpms. I'm running an upgraded Bosch diverter valve and the stock TIP. After the sound appeared I also did a full timing belt/accessory belt, water pump etc. change.

Here's a link to a short video where you can hear it: clicky

If you ignore the sound of rain, the wipers and my squeaky wet rubber soles on the clutch you can hear a wouuuu-wouuuuu sound.

Any ideas would be appreciated. Thanks.

[Mr_Goodkat]

Rain and wipers doesn't make it the greatest audio to try and figure out. However it does sound similar to a potential wheel bearing going bad.

[okhan]

I've heard bad wheel bearings before and usually it's a grinding sound that may change pitch as you speed up, but doesn't just appear and disappear at certain rpms. Isn't it?

[Bische]

I had the same sound when my stock DV took a crap

Do you have a boostgauge? I think it sounds like your sound apears at a certain boostpressure/flow, not a certain rpm. As in the last try you could hold the sound out with some more gas, as the rpms climbed.
If you have another or can borrow a DV for 5mins, try change and see if the sounds still there. If you dont a have another DV, you could plug the hoses a go for a testdrive, but dont go fast and the furious that way

[b6onboost]

It is likely the DV making the sound right around the -5inHg to 0psi range. This is when the DV can be slightly open just before you begin to build boost. The air just barely sneaks by the piston or diaprahm making a sound similar to blowing on an empty coke bottle. It is common on diaphram style DVs like the Bosch 710n and APR R1. The sound can come around on piston style DVs too if it isn't lubed and is sticking a little.

Check how the valve was installed. Audi began reversing the DV orientaion due to costomer noise complaints. It is possible that simply flipping it will make the noise stop. If not it's probably torn or on its way out. There are plenty of threads on DV orientaion, ie reversed vs not.

[okhan]

Thanks for the replies. I was hoping that it was only the diverter valve, although it's a brand new 710N. It's definitely a "blowing into an empty coke bottle" kind of sound.

I have a used Forge 007 that I was thinking of trying out. I'll try installing that and hopefully that will cure my problem.