Weird noise when accelerating


I have Golf 4, 2001, TDI PD 110 KW (150BP)

So i have a problem. My car is making some weird noise when accelerating. It happens around 2,000 RPM ± (and only there). Its only happening when i am flooring it. 1,2 and 3 gears only. Engine isnt losing power, turbo is pulling, no RPM loss or drop. The sound is exactly like you would throw cat in your engine (i am not kidding) - it is like howl or whine. If i am accelerating normaly/smoother its ok, it happens only when full throtle. It does nothing when its in neutral and i rev it, only in these gears when full throttle. Does anyone know? Maybe some leak? I know its hard to help like this, i just need some way to look so i can start to cut stuff that arent the problem. (sorry for my english)