Noisy A6 v6 tdi

Hi
I feel that there is a lot more engine noise recently on our A6 v6 tdi to the extent that you can no longer hear the whistle of the turbo, if I stop the engine,wait,disconnect the battery reconnect after about 2 mins (to reinstall ecu engine settings by default) she then purrs like a pussy cat,runs a lot quieter,smoother and you can hear the turbo again this last's for about a week and then the engine becomes noisy again! /ubbthreads/images/graemlins/confused.gif
I think it might be a timing problem but why it keeps slipping and then is fine when reset is beyond me /ubbthreads/images/graemlins/crazy.gif
Any other ideas?????
I Live in rural France, plenty of "Red" but no vag.com and at least a 3 week waiting list at the local Audi garage! who Honestly I don't have a lot of faith in!

cheers for the quick reply! /ubbthreads/images/graemlins/ok.gif

1998 2.5 v6 tdi
can't say that I've noticed any change in engine noise with air con on but will go and try.
It's just a "Hi I'm a diesel engine noise" but trice as loud sort of "growling" noise with a slight deterioration in performance!