[MikeStatesville]

To add to what Jack said.

First, I totally agree that the S60 is a LOUD engine, especially if standing directly behind the engine. Lots of gear noise. Could you be hearing the turbo whine?

Do you have the huge 50DN alternator or a normal size alternator?

I have a small alternator.  I tried the screwdriver deal to listen to various components, hydraulic pump on front of engine, gears, alternator. No joy. All good. Is there another hydraulic pump somewhere?  I can hear a whine while standing at rear of bus.  Not turbo whine, I am familiar with that sound.  Thank you for your input!