On certain vehicles, the torque converter and the ring gear are not properly welded, and repetition of acceleration and deceleration etc. can cause the welded sections to come apart, in which case the ring gear and the mission case may interfere with each other making abnormal noise. If the vehicle continues to be driven in such a condition, the ring gear may break, damaging the oil cooler pipe, which could allow oil to leak and in the worst case cause a fire.