1995 C1500 Suburban Alternator Problems

Hello,

I have a 1995 GMC Suburban C1500 2wd. I replaced the alternator about a year about with a reman unit. Recently, I have been getting an evil grinding noise from the alternator. When looking under the hood I notice the black fan (right behind the pulley) is rubbing up against the outside of the alternator. Sometimes it'll happen and sometimes it'll just go away. I tried bending back each fin just slighting so it does not grind against the main part of the alternator.

Why is this happening? And How can I avoid it from happening again?

Thanks for your help!