Been fighting with a noise problem on two vans for 5 or 6 weeks.
Sounds like any number of bearing problems but in the end the problem was
the drive shaft on the alternators were slightly bent.
Easy to tell. Remove the serpentine belt and hand spin the alternator drive
wheel. If it is not true (and it only needs to move a hair out of line but
the movement is visible) the alternator needs to be replace.
One warning. If you go with a rebuilt alternator check the drive wheel
before you take it home as we had several rebuilt units that were bad from
the get go.