I removed the blower housing from the dryer, and washed out the lint, dried it off, and replaced it. I was also able to re-assemble the blower housing and put the fan back on the shaft.
However, the blower fan was hitting something at one location as it rotated. I adjusted the motor position slightly until the knock disappeared. But when I reinstalled the drum and belt, the noise returned. I removed the drum, tried more adjusting until the fan rotated quietly, put the the drum back, but the noise was still there.
Couple of questions-
1) how much shaft should protrude beyond the fan retainer? Right now, it is about 1/8".
2) how much of the black plastic coupling ring on the fan side of the motor should fit into the retaining ring next to the blower? There is a shoulder on that black coupling ring, but it is nowhere snugged up to that retaining ring/clamp. There is roughly 3/16" between the clamp ring and the shoulder.
Any other suggestions appreciated.