307 hdi this is the last chance(sqealing on boost)

[rapidshed]

ok not got much of a choice here as cant sell it in current state so gotta do more trips to garage to find a fault,

unblock diesel filter, followed by anti pollution fault,

cars had new diff sensor, cleaned out the filter with mr muscle, new pipes for fluid, and drove spot on for 25 miles now all back again,

can it only be the filter left to change i dont want to throw another 150 at it for no reason

and on boost its sqealing so loudly after 2500rpm, its never done this before this is a new fault yet another one, what could this be?