Alternator bearings, but you have already said this!
Just get a new alternator, not hard to fit, one adjusting bolt and a long fixing bolt to remove, work from the bottom of the car upwards. Easy enough job Id say 1hr for a novice mechanic. Replace the belt as well when your at it. They are only £4 - 6 and you then know its been done.
PS You can tell when a belt is going as it begins to fray around the edges and the teeth begine to crack (rubber fatigue) If you push on the top of any belt you should be able to push a finger nails tip length down. This shows it is the correct tension.
Any help you need PM me.