Hello, I hope I can offer you some assistance.
From your description this is likely to be a split in one of the turbo system pipes, the noise you hear will be the boost pressure escaping from the split. Check all the rubber hoses for the turbo especially the small elbow section that connects to the inlet manifold
as this splits underneath. Look for any signs of oil loss that would indicate where the hole/split is.
Let me know if I can assist further or if you have more questions regarding this and I'll reply as soon as I'm able to.
Thanks for your response.
Have spoken to a diesel expert and he confirmed that your answer seems plausible , especially with the other issues like loss of power. He also asked if there was any black smoke and there has been so more than likely its the problem you identified.
Won't know of course what the issue is until its looked at but am happy with the response- thanks!
let me know if I can assist further.
Got the focus looked at today and the problem was exactly what you said it was!
Great support since a lot of garages would look at the problem and not know what was the issue.
Hi, glad I could help.