When I sold spark plugs at the parts counter
we would get tons of people who bought inserts/blades and the like. Many could not install them or they bought the wrong size so we would replace or refund the purchase. Now the packaging was ripped open so they were almost impossible to sell so the employees would get to take them home. I have or had dozens of blades and inserts and full wiper arms too and the Bosch were way overated and overpriced. Trico was fine and Anco is good too and much more reasonable.
As far as the chattering goes, my wiper motor was defective and would do this and also not stop on the bottom of it's arc. I recently replaced the motor and no more chatter.
current and or past: 1987 Milano (Ariel) 1984 GTV6 (Sabrina) 1992 164L (Jill) 1992 164S (Kelly) 1989 Spider Veloce (Julie) 1991 164L (Chris) 1991 Spider (Melissa)