It also depends if this is happening during a mode change (from fwd mode to side mode or reverse) as the steer system gets fed pressure from the manual valve chest. Is this happening during normal operation in one mode? Or when trying to switch modes?

If its happening during mode change and there is a high pitch squealing (steer system going into hydraulic pressure relief) I would inspect the steering prox sensors for proper operation first before anything else as this is the most common failure. (Clean, set air gaps and make sure they are lighting up when in front of metal) I also forgot to mention to check the wheel stop bolts for proper adjustment as this would prevent the wheel from stopping in the correct position physically.