I had the same (or similar) noises when I first purchased my car. I had tightened a couple of time with temporary success.

It turned out that either the incorrect # of shims were installed or the nut was loose because when I took everything apart I noticed that the washers or cap had carved a groove into the keyed protrusion on the fan...actually on the yellow chromate piece that's riveted on the fan. As a result it was not possible to center and tighten the fan properly. Had to get a new one.

I'm going from memory here so I hope I'm not totally off with describing the "keyed" protrusion.

So I did more than rebuilding my old Marshall 70A alternator... I replaced the complete alternator. I bought a Bosch Paris-Rhone 75A alternator with integrated Motorola voltage regulator. I had to modify the air guide behind the alternator in order to have some room for the integrated regulator. I removed the previous external regulator (for sale... make me an offer! :p ). I had to slightly grind the small "cover" that goes over the shims because the shaft of the new alternator was slightly larger than the old one. I installed a new belt, added a 6th shim (I initially had only 5) and everything is running fine since then.

Gee... I like to work on that car! I don't have lots of experience but I like it!

Alain

I just changed my alternator this summer because of a rattle in the alternator. The bearings had worn a slight groove in the shaft and were failing. I ended up replacing the entire alternator. But now other than my Dansk, I have a quiet car.