clay bar the window using the same clay bar and lubricant you would on your paint. Audi turned my onto this. when i had my A4, there were brochures at the dealer to send away for a free "winshield kit": clay bar and lubricant - which is just a detailer's mist. (spray wax used for a quickie polish after washing).
as with paint, then clay bar will remove invisible contaminants that cause the blade to ride roughly on the glass surface. sometimes the build up is worse depending on where you live, climate, etc... this is the best, most consistently reliable fix i've found for chattering wipers.
it will get the windshield so clean that at highway speeds, the water will bead up and roll off as if rainX was applied - probably due in part to the lubricant. but rainX can agitate the problem if you're putting it over a windshield with grime on it.
i've used meguiar's, 3M, and mother's clay bar kits. be sure to use plenty of the lubricant. it takes less elbow grease than you might think. spray a section of the windshield, rub the clay bar back and forth a few times. move on until the windshield is done. use a towel to wipe everything up and the wash the winshield with glass cleaner.
if you've never used clar bar before - wait until you try it on your bumper after a bug filled highway drive. wash the bumper with soap and water to get off the major krap. spray on the lube and wipe with the clay bar. way more effective than bug and tar remover products and takes less effort. clay bar does remove wax so be sure to put a coat back on the paint after using it. i typically clay my cars at least once a year in the spring after the "winter salt season". i'll do the nose and behind the wheel wells more as needed. claying provides a smooooth clean bas for polish and wax and really helps to bring out a nice, deep shine.