Re: Skipping & Chattering wipers.
I don't know about the 147, but the 156's wipers seem to suffer from juddering and noise in light rain too, especially with the rain sensor fitted as it seems just a tad too keen. My wipers are defiitely worse after a winter where there was sometimes ice on the part of the screen, maybe it wore them out.
On the 156 the tip of the driver's wiper can (just) hit the rubber glass surround as well, both my 156's have done this.
I use glass polish, I even tried Rainx-ing the glass just on the last part of the driver's wiper's movement, to no avail (it's this part that causes the noise). I think the heavily curved and raked screen makes life difficult. I've used Bosch wipers on other cars with great effect before, the better half's Focus has perfect action, probably as it has a flat screen!