Wiper Problem

[raceboy]

Every now and again my wipers refuse to stop wiping, intermitant wipe is not intermitant, normal is normal, and fast is fast, but off, is still wipe wipe wipe, looks a bit silly when you've just switched the things on for a one quick wipe of the screen
Problem is it only happens intermitantly so I imagine something is loose somewhere, anyone got any ideas?