I have a 2014 388 with a 600 cummins with a 18 spd 2050 . There is a rappen or knocking noise in the transmission when pulling a loaded trailer. You can hear the noise after you have driven about 50 miles bobtail. Notice the noise when you accelarate bob tailing or loaded every gear. Press the clutch petal lightly, the petal really jumps under your foot and noise is louder. Press the pedal farther , pedal smooths and noise stops. The truck has 42000 miles on it. Noise would come and go since new . Now noise is constant under load.