I was out running around in my car today and was on the interstate ging through some gears. I was getting off the interstate and my car locked up in 4th. I about had to beat the shifter out of gear. It shifted into all the other gears fine except for a clank in 3rd. On the way home i locked up in 4th again but shifts easy in it sometimes. What kind of problems would cause this. Also, it seems like there is a vibration in the drivetrain somewhere.