Well yesterday I drove about 50 miles and then pulled in front of a friends house. I left the car running. Their driveway was on a little bit of a slant, anyway we talked about 15 minutes and off I went. When I pulled out in reverse a huge cloud of white smoke came out of the exhaust. I pulled over and it was gone. I drove around quite a bit that day and it never came back. Anyone know what this could have been? Thanks!