Need help with identifying a noise

2007 Sonata 3.3L V6.
This noise is from under the hood, and I can pretty well localize it to the right side of the car and toward the front. My best guess is
something that gets driven by the serpentine belt or the belt itself, but I don't know what.
The noise is a whirring sound of low to moderate pitch, which rises and falls with engine RPM. It is virtually inaudible at idle (600-ish RPM), and is best heard at and above 1300 RPM or so. It is drowned out by road noise at any speed over roughly 40 mph. The A/C being on or off doesn't affect it one way or the other.
A quick punch and release of the throttle seems to cause the headlights to dim noticeably for a second or two as the engine returns to idle. I hooked up a code scanner device to the car the other night, and noted that the voltage it read dipped to about 13.5 V with these quick punch/release cycles on the throttle.
This is about the best I can do at describing it. Anybody have any good guesses?
--
Larry Harvilla
e-mail: larry AT phatpage DOT org
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On Thu, 14 Oct 2010 07:39:28 -0400, Larry Harvilla

You didn't mention your mileage as that may help. My guess is a shot but it might be the serpentine belt idler pully. You might want to have that checked 'cause if the tensioner is weak or failing it would cause the belt to slip which might be causing the drop in rotational speed and the subsequent lower voltage output from the alternator.
Just my $1.98 guess. But please post your findings when they're known?
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Good a guess as any. Alternator bearings can do such a thing also. See if you can use a "listening device" on each item turned by the belt. Anything that will telegraph the sound will do, just don't stick your fingers near the belt. Long metal rod or screwdriver can help.
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