rathesub

I have a 91 Subaru Loyale with push button 4-wheel drive. From time to time, my 4WD comes on without me pushing the button. When it does so, my car drives very differently and pulls to the right. While this is a problem, it is not the big worry. What ends up happening is that once this happens, I try to pull over and turn off the car. Normally, as I am trying to do this, my car makes a big thunking sound and it feels like I ran over a massive rock. Then the 4WD stops and it begins driving normal.