The intervals on the wipers are known to stop working
after a while. When on slow intervals the wipers starts
missing a sequence and makes strange sounds. This will slowly get
more and more frequent until the slow intervals don't work
This is a common problem, but this could be your solution:
Unscrew the wipers, then the plastic cover.
On the drivers side you see the engine, take the cover off.
You see wires coming in - disconnect then you can with the help
of screwdriver open the part where electrical thingies meet
engnine (you will see it).
Problem is that there is a lubricant that gets stuck to
electrical parts of that wiper engine and thus stops the
movement. Solution is simple - just clean it and put it back togeather.
I wan't to add that this is a common problem with all new Alfas (155, GTV, Spider..)