OK, I miss-diagnosed the problem. At first, I thought it was a loose fan. But when I reached in back and moved the fan, it had what felt like a little up-and-down play, but didn't seem loose. The more I listened to it, the more it sounded like a bad bearing. Jason stopped by the other night and as soon as he heard it start up he said it sounded like a bad bearing. So, I ordered the bearings. I figured the play I felt was wear in the bad bearing.
I just pulled the fan shroud and took the fan off. When I got it out where I could see it, it was obvious that the fan was, in fact, running loose. But, the nut was super tight! :-k That didn't make sense until I finally got the nut loose. The fan wasn't loose, it was broken. The very center part was locked in place like it should have been and about a half inch out from the center there was a hairline crack . . . luckily it wasn't in a perfect circle, so it kept the fan turning. The good news is because it was tight in the center, it didn't wear out the spacer. The better news is I don't have to put Chineese bearings in my German generator.
RetBugtech . . . have you ever seen one break out near the center? If so, any idea what might have caused it?