Windshield wipers

If the chattering only occurs when the wiper arm goes up or down, but not both, you can put a slight twist in the arm to change the angle the blade sits at.

If the problem never occurs when the blade is new, it may be gumming up with bug juice or road tar. When I worked for a very nice Chrysler dealership, they had a product called "Total Clean" that could be poured onto a clean paper towel, then used to wipe the blades clean. A more aggressive version of that was called "Super Clean". Both are a soap in liquid form. Total Clean is meant for fabric. Super Clean works great for road tar and rust-proofing over-spray.