I have a 2002 Mercury Mountaineer AWD 8 cy. We drove about 2 hours the other day. When we were almost at our destination we went over a hill and noticed a hissing noise. We thought it was a tire so we pulled over and checked. Not a tire. So we got back in and turned the car on and put it in gear and the car would not moved. We tried pushing it, no luck. The front tires were locked. We had to have it towed. When the guy brought it back today he thought to try it out to see if any difference and the car moved into reverse and drove backwards. So I tried it in drive. It went forward. We had been having problems with the CVjoint. There was a clicking noise whenever we would turn to the left. What could this be? Could it just be the CVjoint? Or is it maybe the transmission?