You could try swapping over your LUC solenoid with one of the other three ‘black cap’ solenoids if you wanted to prove a point



but it’s much more likely to be wear of the LUC friction plate that’s causing the issue. Range Rovers use the same Sachs WA4/W260 S-2GWK (F38 model) torque converter and usually start with the ‘cattle grid’ noise at just over 100k miles.



The travel of the LUC apply piston is only around 1mm so it’s very sensitive to wear. On the Range Rover the transition from continuous-slip to full lock-up is at around 57mph



Phil