Thanks for all of your responses. I had the opportunity to deal with the noise problem this morning.

Disconnecting the mechanism from the motor did not quiet things down and the wipers moved freely by hand after they were disconnected. The noise, however, remained the same.

My experience with loose magnets was that the motor ceased to function. As I took this one apart I found both magnets to be in place, but one of them came off with very little effort. I tried to take the other one loose but even moderate prying with a screwdriver failed to dislodge it. I used epoxy to glue the loose one and then put a little epoxy at each end of the second one to "weld" it to the case.

Pulling on the case and magnet assembly pulled the armature out enough to allow the brushes to move off of the slip ring so I went ahead and pulled it all the way out. I cleaned up the surfaces the bushings ride on and applied some light grease.

I put some grease on the worm gear as well as the large circular gear. They were dry and I think this is where the noise was being generated (I could have lubed that area without removing the wiper motor from car!)

Those three brushes were a bit tedious to work with. There are spring clips that hold the springs in place once they are pushed in behind the brushes. That was a nice touch but getting the spring compressed and down far enough to snap the clip in place was a challenge. One shot out and bounced off of my chest. I was lucky to find it as my work area is cluttered. If I ever had to do it again I would move to a more sterile area which would increase the chances of finding a stray spring and/or clip.