whining noise from alternator when starting car?

[MusicIsLife]

ok, so ive had my truck in to a shop and just found out that my alternator is going out and needs to be replaced sooner than later. However, ive just recently made a connection between my bad alternator and this whinning noise ive been hearing for the past couple months when I start the car. Itll last for about a minute or so then die out as the engine warms up. sometimes it will come back for just a few moments when I start moving but then go away for good. Ive had no idea what this noise was until i started it one day and poked my head under the hood immediatley afterwards, and i could definitly tell that the noise in question is in fact coming from the alternator.

so my question is, what is the noise, exactly? and is it a sure way of detecting a failing alternator, or is it a defferent issue alltogether? just wondering for future reference...

thanks!!!
ok, front pulley bearing and alternator bearing: are these the same thing?? and do these bearings come with the new alternator or are they seperate from the actual alternator??

 

[LAB RAT]

Whining noise probably means that the front (pulley) bearing is starting to go.

 

[Jerry]

The alternator bearing is going out. Change it before it freezes up while driving and tears the entire belt off. Like right now.

JJ