Whistling noise on cold engine

[GTamas]

Hi everyone,
My 94 GT started recently to do a whistling or whining noise when starting the engine cold. It does it only at specific rpms, around 2000 and 1100. The pitch also changes slightly with the rpm. It's coming from the engine bay and it's not super loud, but easily hearable. I have the feeling it has to do something with air currents. Sounds like blowing a whistle.
It goes away when the engine is warmed up.

There's a video below:

I did not yet have the chance to locate the source because it does not do it at idle and I did not have anyone around to set the rpm while I look for the source.

Do you have any idea what I should look for?
Engine is stock with only a K&N filter inside the stock air box.

 

[ttocs]

check the pcv behind the lower intake to ensure it is in tight. I had the same kind of noise that drove me nuts for a while because no matter what side of the motor I was on, it sounded like it was on the other side.

 

[GTamas]

Thanks, I'll have a look at it.

 

[SnakeBit!]

vacuum leak? smoke test?

 

[cobrajeff96]

Might actually be the throwout bearing.

Noises are especially difficult to pinpoint in a giant metal echo chamber.

 

[ttocs]

that pcv whistle drove me nuts going back and forth. I was starting to think it was moving every time I moved.

 

[GTamas]

I hope I will get the chance to do a smoke leak test soon.