I am having trouble with my nissan sentra 2003. it is making a loud noise around the alternator.its a loud noise which sounds like the alternator belt is scraping or scratching on something.
If the belt is loose it can make a squealing noise. If the alternator bearings are bad they can make a noise such as you describe. I think it’s time to have the alternator checked.
When was the last time the serpentine belt was changed? A worn out belt can make all sorts of nasty noises. I change mine every 3 or 4 years. If it’s the original belt it’s due to be changed. Hopefully it’s the belt and not the alternator.
Take off the belt and check all the pulleys. It might be as simple as an idler or tensioner pulley. They only cost a few bucks. You seem to think it is the alternator, however, so it probably is. My FEAD belt is 10 years old with 100k+ miles on it. I think I will replace it though it looks good. I know that the idler and tensioner pulleys will be replaced too. They are identical and the bearings on one feel a little gritty.