FOOTHILLS RX7

A few days ago a pop or a clank sounded when I turned the corner in first gear and then it sound as if a universal joint was clanking. However here is the rub. The sound does not happen all the time just once in awhile and mostly when turning a corner in first gear. It sounds alittle in second gear, none in third and fourth. I do not have any vibration on the highway. I took it by a shop for an expert to listen to the sound and of course it didn't do it. He said it could not be a universal joint because it would do it all of the time. Do you guys have any ideas on what it could be. Don't hesitate to ask questions if I didn't give enough imformation.