Now I think I really do have a wiper problem!

The wipers seem to be all over the place, on Monday (Leeds) I was driving with the wipers set to intermittent. The wipers were going all the time, in fact they were going really fast, as if I had the wipers on the fastest position. When I stopped at a traffic light, normally the wipers stop too, the wipers kept on going at the fast speed. I switched off the wipers as it stopped raining, and when it started to intermittently rain again I switched the wipers back on to intermittent setting. This time they worked correctly, when I stopped the car the wipers stopped and when I set off again they went back to intermittent wipe.
My question is this could I have a faulty sensor? Why do the wipers go really fast when I am not? Will VAG be able to pick up the fault? Any ideas, apart from the obvious Stealer Visit?