VGT's make a very peculiar sound when we give the engine some throttle and then pull off. If i may describe it so, it's like a 'chhoooo' . I've not noticed this much when driving, but once or twice when i gave it some throttle at idle then this sound was there. Since day one. If that is the sound you are talking about, then it is perfectly normal. Recently i had the opportunity to drive a Punto FGT on a long ride and found that it's turbo is much more vocal than the VGT's. Cheers.