My friend has a stock 02' passat 1.8t and is experiencing a loud hissing noise (sounds like shhhhh) under acceleration. The noise is particulary loud as the turbo is getting into boost and as it is boosting. Normal, non boost driving does not produce the noise. Originally, when she bought the car(~50k miles), it did not make this sound, but now that its at 75k its become quite loud. Also, I would say that drivability has gone down with occasional hesitation, a feeling of power loss, and a non linear boost delivery. Ive read a number of threads already and they all seem to point to hoses, but I thought that this noise was probably a defective diverter valve. Where do I start and where is this sound coming from? Someone please help. Thanks in advance.