Ford Focus 1.8 tdci hissing noise

[Micknik]

Hi there I have a focus 1.8 tdci on a 06 plate the last couple of weeks while driving I have noticed a hissing noise that has gradually got louder and have noticed a big reduction in fuel consumption. There doesn't seem to be a problem with it boosting but when you power off you get a loud hissing noise also if you put your foot down you can hear it at high boost. There is no white smoke although at high revs I have noticed some black smoke been told off a friend it may be a leaking hose. I have had a look under the bonnet and there are that many hoses I wouldn't no we're start it does seem that the hissing noise is coming from the back end of the engine rather than the inter cooler end... Any advice on which hoses to check or tips to try and diagnose the problem any help would be much appreciated... Thanks

[sunbeam alpine]

Turbo hose split.

[Camaro]

Yep, turbo hose.

It may be impossible to spot as it'll probably be a tiny slit but it'll be leaking.