mine also is noisy over 3000 rpm. Been to several garages for diagnosis. diesel specialist says its not turbo - ford say it is.local garage says big ends- next says injectors or pump,not enough mileage for big ends.Warranty company not interested -got to be a complete breakdown.Had the car 6 months now- the noise hasn,t changed at all. I only hear it when the front windows are open. Learnt to live with it.The only way i can describe it is like a piece of cardboard rubbing on the spokes of a bicycle wheel !
If the turbo makes any noise at all, it will be a high pitched whistle. Most modern automotive turbos rev so highly that the frequencies they generate are beyond the range that the human ear can detect. You may be able to hear them spool up as you accelerate, but the noise should then disappear as the revs rise. You will be able to hear turbos on trucks and other large machinery, railway locos etc more clearly, as their turbos don't rev as fast.
If other noises are present, but not getting any worse, I would be inclined to just live with it. Modern engines are very well soundproofed and great care is taken over their installation to ensure that noise is not transmitted into the passenger cabin. Such things as a poorly installed replacement exhaust can cause such a transmission of sound if the hangers are under too much tension for instance. Engine mounts in the process of failure can also lead to transmission of noise under certain circumstances.
If you're regularly in the habit of taking a Diesel beyond 3000 rpm, it will be noisier than a petrol engine. Unless you're really pressing on, such rpm are really not necessary as modern Turbo diesels produce their best torque between about 1600 and 3000 rpm. That being said, a good blow-out now and again will help to keep all the gas passages free of carbon deposits, which can lead to turbo problems in the long term.