Need Ideas To Diagnose Source Of Noise

[DouginDenver]

'02 S60. Makes a whirring sound from the engine compartment that increases with engine speed. It does it in park or neutral as well, so it's not a drivetrain issue. It's a sound I would associate with an accesory with a bearing going bad. I had it at the dealer to make a new key, and they said my serpentine belt idler was bad, so obviously the dealer also thinks it sounds like an external accessory with a bad bearing. I replaced the idler myself and nothing changed. So it is something else, but how do I isolate it? If I take off the belt and start it and the noise is gone, all that tells me is what I think I already know - some accesory is noisy. I tried the screwdriver to the ear trick on the ps pump and alternator, but that was just so much mechanical noise I could not single out anything - sounded like I had my head under a subway train. So what is the procedure to figure out which accesory it is?