Flutter sound

[John williams]

Hi I'm looking some help and advice. I own a audi a6 2.0 tdi sline, is a 2007. Last year the oil pump failed with no warning  (common fault) which resulted in the turbo and other parts needing replacing. At a cost of £5k. Audi paid for half the work they fitted a new system different to the 1 with the common fault. My audi is a 7 speed auto it now makes a fluttering sound when its moving in drive. Does anyone have any idea what it could be please?