My turbo starts squealing making a sound like a worn gearbox when i ease of the revs and it drops to 3000 RPM. Noise only lasts for about 2-3 seconds then goes again. It is fine whilst i am increasing the revs and is driving perfectly. Ford Mondeo 1.8TD
Sounds like the bearings in the turbo are going. A very common fault with turbos. I know someone who had a Laguna turbo-diesel. The bearings in the turbo went and went through the cylinders. �4,000 of damage (at Renault prices), not to mention a new turbo.