Ok I have this problem. When I pull out of my drive way, I put it in reverse and sometimes it just sits there with out moving until I press the gas a bit, and just before it moves it makes a loud metalic "knock" sound. Then when I put it to drive it does the exact same knock. What could it be? I have a rebuild tranny and new torque converter. Someone said it could be the U joints. Any advice would be highly appreciated. Be a pal and help out a poor bird lover.