Audi A6 2002 2.5 v6 tdi

[Tkz1000]

Hi to all I own the above car which has done nearly 300000 miles but one last fix before we say goodbye problem is the turbo is making a banging backfire noise into air box have checked basics turbo not seized wastgate seems to be working and all pipes connected I know the boot from the bonnet but am no mechanic thanks for your help. AUDI A6 AVANT 2.5 V6 TDI 2002 ESTATE 

Edited January 2, 2020 by Tkz1000
Forgot to put full model