My car recently developed a very annoying, high pitched whine coming from the turbo area while under vacuum. Has anyone had this happen and any idea what the problem is? The stronger the vacuum reading the worse the sound is, so under engine braking and idle it is the worst, and then it gradually disappears as I get out of vacuum under acceleration, disappearing by the time I get to 0psi. No other symptoms that I can tell. At first I thought it was a shot primary turbo, but the car still boosts normally and no oil leaks or smoke, plus it seems odd that the sound only occurs under vacuum. I'll be taking the car in to get inspected but I thought I'd get some feedback until then.

 

I'm guessing a vacuum leak. These can often sound like a "whine" or a "whistle." They can also resonate like a turbo sound depending on where the leak is. IIRC, I read about a gasket leak in the intake manifold assembly causing a noise like this.