My turbo started making a high pitch "whistle" or whining noise a few weeks ago, especially when accelerating in 1st, 2nd and 3rd.

At first, I could still hear the turbo boosting and it seemed to be driving okay. However today, there is a whining noise that has suddenly become MUCH louder and happens consistently even when touching the accelerator lightly. When revving in neutral, I can also hear the whine. It's an "air-y" sort of noise. I can't really hear obvious scraping coming from the turbo but it's really hard to tell. 

Is my turbo stuffed? Thanks. 

Caitlin, I noticed you're in Adelaide. There's an A4 B5 Forum here in Oz. https://www.facebook.com/groups/1910376765662134/ 

You might find or ask there for recommendations where to go, if you need someone to do it.

Your Turbo to Exhaust Manifold Nuts might have loosened off. Whistling sound is air escaping from somewhere. Is there an exhaust smell or blackened area? Look with a mirror or an inspection camera. Careful - it's HOT!

Invest in some Nordlock Washers and retighten the nuts. There just might be a vacuum leak causing the whistling sound. The gasket could be gone too.

Look here to see if this diagram matches your engine code. (I took a guess) The Nordlock Washers go under the Nuts that Screw onto the Stud #4

https://audi.7zap.com/en/rdw/audi+a4+s4+avant+quattro/a4q/1999-224/1/145-145060/