Why does the turbo on my diesel whistle so much?

I recently had my engine and turbo replaced on my Vauxhall Mokka. I am not car savvy and had been on my way to a garage to get the high pitch dentist drill noise checked out. Once I had the car taken to the supplier I waited a month to get it back. When I received it back it was working brilliant, but recently it's starting to make the dreaded whistle again. Is it normal for a turbo to whistle all the time? This is my first diesel so I don't know if it's a normal thing. This time I cannot tell if the noise is noticeable from outside, whereas last time you could hear me coming a mile off with the siren sound of the turbo. It does not make the noise when idle only when accelerating.

Asked on 31 January 2019 by Greg

Answered by Honest John
The original turbo probably failed due to oil starvation of the turbo bearings because the turbo bearings oil feed and oil return pipes were blocked with carbon from switching the engine off when the turbo was too hot. If these pipes were not replaced at the same time as the turbo then that explains the short life of the new turbo.
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