I just replaced my wiper inserts with OEM replacements (I have sworn off aftermarket insetrs, because they only last 3-4 months compared with 6-9 for OEM), and I have the same issue - on the up-wipe, they are chattering pretty bad, even with a lot of rain on the windshield. I think they will settle in with a little use, but who knows.

I'm a huge fan of Rain-Ex, too ("The faster you go, the better it works!"), but have recently switched to Rain-Ex brand wiper fluid. It's the milky orange stuff, and it works great! Hard to find, though. But basically, it refreshes your Rain-Ex finish whenever you use it. Good stuff!