tranny troubles

96 corsica with 3 speed auto.2.2L In reverse or first, tranny makes metallic popping sounds with the vehicle lurching. At slow speed (less than 5mph), it will actually stop the vehicle. If you accelerate, it will shift into 2nd and noise stops.Downshifting into first from 2nd the noise comes back. Tried the c-v joint check of driving in circles--couldn't tell. Any info would help....

Thanks!