you may have the rain sensing wipers, which i personally don't like. i can turn them on myself. anyways...if you do, and if it's anything like what i used to have in a vehicle, when in that mode, they would wipe once when you turned the car on - kind of a 'check' to ensure they are working.
if you don't have the rain sensing wipers...may need a trip to the dealer for some diagnostics and warranty repair
I have the rain sensing wipers and I leave them off until it starts raining. But, they still seem to have a mind of their own. Certainly, not related to the rain. They will barely wipe at the most sensitive setting and then wipe too much when I'm stopped. Or wipe on full speed when I pull away from a stop. Very frustrating.
Mine work fine except when it stops raining they don't seem to notice and keep on wiping intermittently. My guess is that the glass is still damp and this triggers the sensors.
Oh, and I was driving in heavy rain recently and even on full tilt the wipers were not very efficient. Seemed a little slow. I, and several other drivers, pulled over to the shoulder until it eased a bit. I also had to figure out how to use the rear wipers!