Few automotive problems are more annoying, or more preventable, than chattering wiper blades. Wiper blades chatter when, instead of sliding across the surface of the windshield smoothly and easily, they jump and skip across the surface, making an annoying sound and leaving the windshield dirty. This may be caused by a bent wiper arm. Wiper arms have to be positioned squarely over the windshield so the wiper blades are in the correct position with respect to the windshield surface as well. The solution is simple: bend them back into place.
Remove the wiper blade from the wiper arm. One wiper blade or the other may be the problem, but it is wise to both wiper arms to prevent issues from arising later on. Set the wiper blades aside for now.
Lift the wiper arms up off the windshield surface and look down the length of the wiper arm to see which direction the wiper arm is twisted.
Fold a cloth rag and lay it onto the surface of the windshield. Let one of the wiper arms rest on it so the arm does not scratch the glass. Slide one crescent wrench over the flat part of the wiper arm at the middle of the arm. Place the cloth rag under the middle crescent wrench to protect the glass. Slide another crescent wrench over the end of the wiper arm.
Twist the wrench on the end of the arm in the direction required to flatten the wiper arm with respect to the windshield. Remember that the wiper arm must be parallel to the surface of the windshield.
Reinstall the wiper blades onto the wiper arms and test the blades for any residual chattering. Make further adjustments as needed.
If wiper blades still chatter after straightening the wiper arms, replace the wiper blades with a new set. If the wiper blades still chatter after the wiper blades have been replaced, the windshield may have a contaminating film on its surface. To find out, wash and dry the windshield. Slide your hand into a plastic sandwich bag and run your fingers over the surface of the windshield. If the windshield feels rough and grainy, the windshield surface is contaminated. This contamination can only be removed with a clay bar and a clay lubricant product.