I replaced both bearings today but the noise continued unabated. My son discovered the actual problem. Because my rims are only 20" diameter, I was unable to spoke the wheel and elected to add four oak wood spacers between the PM and the rim. One of the spacers was creating the noise! Once each revolution the spacer in question would get a slight twist and would protest by making the sound. Tightening the mounting screws and adding extra epoxy ended the problem.
I took several pictures of the bearing replacement process and will post them together with a step-by-step procedure in my next message (tomorrow). It actually wasn't that difficult and would have been even easier if I had the possessed the knowledge I now have in in hindsight!
Michael
