Many people change their wiper blades because they chatter and so they think they're hardened and shot. What causes most chattering is the fact that the long thin flat arm that the wiper assembly is attached to is bent slightly after years of use or being bent accidentally when cleaning the windshield. As a result, the blade is not perpendicular to the window surface and will work fine in one direction but chatter in the other. I've used a couple of crescent wrenches with each one placed on opposite ends of the flat arm and tweaked it so that the blade is sitting correctly.
