Bongo Fury

Random one for you, had some turbo work done two weeks ago and now it sounds 'strange', it doesnt whistle but makes a whirring kind of noise, is this right?
She still has loads of power, not using any oil and returning pretty good mpg.
Any ideas please?

What sort of work was done to the turbo?

Turns out my alternator belts were too tight (hadn't been for long). Still got the from cold low rev 'hoot'