hi i have the fabia vrs pd and have this annoying whurring sound when im sat inside its not so bad when your on the outside , and when you lift the bonnett it seem to becoming from round the back left hand side i dont think its the turbo but could possibly be the cam belt would this cause this sound ???

Could be any of a number of things. Does clutch in/out effect/change the noise? Possible causes are aux belt tensioner, alternator, water pump, timing belt, timing belt tensioner. Can also be caused by air-con if it's low on gas.