It is as quick to check if it is loose as it was to post the question.
However, if you can remove the belt, first check if the fan is loose. If tight, try rocking the blade from side to side to see if the bearings are worn, recondition unit is your best bet.
A spacer is not your problem if it has only just faulted.
Keep us updated for more advice from others!
Sorry for the delay with your question as i have not been on line.
You may have changed the alternator by now, but if you haven't, yes, the bearings have gone and it sounds as if it may have damaged the internal parts of the alternator if it's that bad.
Definately replace this with a reconditioned or new one.
Don't advise second hand from scraps because you need this unit to be trustworthy, plus you get a guarantee with the others.
Just another thought, if you just bought the van and it has a warranty, take it back and insist on them replacing it as it was sold faulty and not fit for its purpose!