Right radiator fan won't turn off..... HELP!!
 

So I took my wife out for the night, we parked the Z and when we came back from the party, we heard a strange noise coming from the front of the car. At first we thought it was a plane or helicopter passing by above us, but then we noticed that it was coming from under the hood of the car. For some reason, the right fan was spinning full speed! We could have sworn when we parked it there hours before, it wasn't on. I open the hood and its spinning full speed while the car is off! Never heard of this. I can't figure out how to keep it off. I've just been pulling the fuse relay for that fan to keep it off when I'm not driving it. Anyone got any ideas on what is causing this? Thanks for any help