It sounds like the turbo has a damaged inner part, the impeller blades can spin up to 2000 times a SECOND and any damage to these special blades will make a whistling noise.

It sounds like the turbo has a damaged inner part, the impeller blades can spin up to 2000 times a SECOND and any damage to these special blades will make a whistling noise.
Smart Car Specialist
Unit 10
Foundation Units
Westfield Road
Slyfield
Guildford
Surrey
GU1 1SF