My 87 MB 190E 8V belt noise again when cold!!!

I just parked my car about 3 weeks. Before i parked, it is no noisy on the belt. When i start the car this morning, it has very loud noise on the belt.
I drove that car over 1 hour, still had the noisy.

If it is the alternator bearing problem, may i just buy the alternator bearing. Or i need to buy the new alternator.

Please help