Audi we have a problem

Please can someone help me I own a A4 2.5 TDI V6 AUTO CAB
I have a whistling comming from my engine when i accelerate it also continues when the engine slows down it is not the normal turbo sound but a high pitched sound. Audi have advised this is normal i dont think it is does anyone have any ideas. Before i take a spanner to my engine. THANKS :1zhelp:

Constant whistling can sometimes be a manifold leak, but if you have recently changed or cleaned anything relating to the intake, fueling, exhaust or management system it can also affect the turbo sound.