I thought that at first too but I'm not too sure that's the problem because sometimes they work fine with no banging. It's like the arms over-extend themselves, but it doesn't happen everytime I use them. Which is really strange haha
I know the wipers are supposed to automatically adjust to what speed you're going but mine are banging off the top of the dash and front pillar.
It doesn't happen all the time which makes me think it could be an electrical issue but I honestly don't have a clue....any help would be great thanks...