After some six month and some ten visits to the dealership, the dealer through in the towel on nmy wiper chatter problem and said they don't know what's causing the problem.
They have already replaced the wiper assembly, wiper arms and blades and cleaned the windshield with every chemical known to man.
As the last resort, they have finally called the specialist from Volvo canada to investigate the problem. His professional opinion was that the chatter is "within acceptable" limits! Like the wipers are supposed to chatter!!
Well, I have asked them for this in writing. I'm planning to give them one last chance to fix this before I take the matter to court or arbitration. In the meantime here are the symptoms:
-The wipers chatter when (and only when) there's water on the windshield. When it's dry it's fine.
-When the windshield is wet, you can hear the blades sticking to the glass while moving.
-The same effect can be felt when I use a wet towel on the glass. Again, it's smooth when it's dry.
-Using the washer fluid, the wipers go smooth for a while, then back to chattering.