On the surface it sounds like a Bearing inside of the Alternator went bad. Depending on where you got the Alternator you could take it back under the Warranty.

Grab the Alternator Pulley and it is loose you will feel that.

Use a Mechanics Stethoscope or some other object like a Broom Stick or long Screwdriver against the Alternator Housing and have someone spin the Alternator Pulley/Shaft and see what you hear.
If you hear a grinding sound you have some internal damage like a bad Bearing.

My Alternator had a Bosch North America rebuild sticker on it and I had to change the Bearings in it. Both Bearings that came out of the Bosch rebuilt Alternator were made in China.

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84 300D, 82 Volvo 244Gl Diesel