any nipple that is undone will whistle. hell i think my alternator is whistling these days, but if its WOT only it sure sounds like a boost issue since the theory of a whistle is BLOWING (though sucking can work) out of an orifice makes the whistle.
i think i got some bad bearings in my alternator (or sigh g-lader) because i hear a small whirr. Then again i have been caught with a boost leak too.
Even though my mechanic did a wonderful job on the !Carbon Canister mod, i have noticed a small whirr ever since.
Lemme tell you theres an unnamed shop that i'll never go to down here again, they tightened down my cam belt so tight that it sounded like a V1 vortec. Thank god the next mechanic fixed it up or i'd have had some sorry ass bearing right quick.
Can you localize the noise to a specific area perhaps? that might help us help you.