I'd check the alternator pulley first - make sure it's able to "freewheel" in one direction; that's a more common issue with serpentine belt roughness.
Remove the belt. Lock the alternator (put a screwdriver in it to prevent it from turning. See if you can freely move the pulley one direction (the freewheeling), but not the other. If it's locked in both directions, replace the pulley.
Replacement is relatively easy in the BEW with the alternator up and front (compared to ALH), but requires a special tool (
Metalnerd for the proper kit, but if time is of the essence, I think Amzn has a kit that'll do the trick as well).