how much end play does the clutch bell have? iv had it happen where when i tightened the screw that holds the clutch bell on the crank its to tight and has no end play, at that point the clutch bell and crank are mated together.
iv also had the clutch bell rub the flywheel, so check for that.
also make sure the flywheel is clean and scratch/gouge free. that can cause the shoes to get stuck.
the only other time iv ever gotten a screeching sound it was coming from the pull starter.