Will be the bsi unit, I had a partner combi where the wipers would work on their own. At first it was just about tolerable and in winter it wasn't a bit issue but I'd the dry even a short journey would be unbearable with dry wipers screeching on a dry screen!

For that iirc they're about £260+ or you take a risk with a unit from a breaker.
Picassos are prone to it apparently.