Gees, I have owned a cat d918a which this apears to be, the CCU is incorrectly adjusted, the screaming you here is the operator engaging the clutch to hold the brake up becuase the cable control unit is not adjusted correctly or the brake band is worn out, the tractor sounds bad to me like bad fuel or low compression as well, look at the smoke coming out when he clutches it, black like it needs air cleaner and or injector work, this tractor should be running dirt over the top of the dozer easily, wish I owned it, would not let it work like this and look like this as well!!!!lol Bad owner and bad catskinner for sure, bet it has not been correctly sercived in years, poor old 18a!!!!