The problem ended up having nothing to do with the freezer evaporator fan or it's components. The problem was that the freezer evaporator fan blades were hitting the plastic fan housing cover. The cover is that angled piece of plastic with the vents in it. I believe this is a bonafide GE design flaw to put the housing really close to the fan, and in a vulnerable place where it can be easily pushed in. The best I can tell is that the fan cover was slightly bowed out when new to keep it from hitting the fan blades. Even still, it's only about 1/8" away from the fan. Over time the plastic has sagged and is now close enough for the fan blades to hit it, and making that awful sound. One solution was to slightly lower the fan motor assembly which also lowered the fan itself and further away from the housing. You can do this by inserting plastic spacers between the fan motor bracket and the plastic shelf it is hanging from. Another option was to heat up that part of the plastic fan cover with a hair dryer or heat gun, and then persuade it to bow out and away from the fan blades again.