Could be everything you talked about that could cause the wipers to chatter because of lack of down force. Also check to make sure the glass is not contaminated with something, clean the glass. I would clean with alcohol first to remove any oils and then I would use Bon Ami cleaner. Damp rag with some Bon Ami sprinkled on it, wipe, let dry to haze, and then wipe clean with dry cloth. DO NOT use Comet Cleanser as the Comet will scratch the glass. Here is link to product; http://www.bonami.com/
You said you replaced the blades but I know cheap blades will chatter too. It seems that about $15.00 or cheaper blades, you run the risk of chatter and going bad fast. Something else that does help with chatter are blades that have, for lack of a better word, wind scoops on them that put more down force on the blade when driving.
I see you're dealing with snow and ice. A tip to keep the doors from freezing shut in ice and snow; spray a rag down with a can of silicone spray and wipe the surface of all the weatherstripping in the door jambs. This repels the water so it can not freeze the door shut and also lubes the door and rubber for a better fit.