As I didn't find anything specific on the wiki or the forum about my wiper issue, here's the solution that the dealer's technician applied.
The first time I went in for this they didn't find any particular problem with the wipers, but they agreed there was a problem with the wipers not going smoothly. They offered to change wipers but I had to come back later for this. OK, few weeks later, another - smarter - technician immediately told that the issue was the wipers positioning (wrong angle) towards the wind screen. Now, wipers are changed and repositioned and everything is fine.
Now, when I looked back at
http://www.civinfo.com/wiki/index.php?title=Windscreen_rattles in the Wiki. Is this the same than my wipers problem? May be a few words extra explanation in the wiki item might help.