I just replaced my generator with an alternator. I kept my original wide belt pulley. Today I took a 150 mile drive and could hear a "whirring" sound coming directly from the alternator. Got home and took the belt off. The bearings sound and feel fine (spinning by hand). I used a cog belt (top and bottom cogs) and had the tension set properly. Could it be that I'm hearing the belt contacting the v groove in the pulley? If that's the case I can live with the sound.