I wouldn't whirr too much about it.
Almost every time I startup I hear a new sound of some description from a cold engine. Once the old bus gets warmed up things seem to settle down.
I sometimes hear a whirring sound from cold that I put down to the steering pump or some other pump trying to do its thing.
Of course the trick is knowing when to start worrying. I used to get a faint whiff of exhaust fumes in the cab when at traffic lights etc. I casually mentioned it to my mechanicand it turned out to be a leaky injectorseal. If left to continue he says it could have wrecked the engine.
