I have a A4 TDI 2004. This problem has probably been covered before but as much as ive searched its not had a fixing solution as yet!

Gradual acceleration upto 2000rpm give a sort of kickback maybe an overboost as i can hear a 'metalicy' spinning noise. This only happens upto 2000rpm.
Its getting worse week after week and I dont really know what to do next.
Ive been to the dealers and have had diagnostic equipment attached but no fault codes are stored......

any help would be appreciated... thanks