I had a similar problem. My fan sounded like an airplane trying to take off. I changed the clutch out, and it ran like it was supposed to.
While swaping them, I compared them both while cool. You couldn't tell hardly any difference. I guess the heat coil in the new one didn't lock up as quick.
It was worth every penny.

P.S. Get a quality, long handle end wrench for this job. Size 13mm if I remember right. <img src="/forums/images/graemlins/kewl.gif" alt="" />