The last 8430 I had in the shop was doing this and the Load Sense pressure was not returning to the correct lower pressure.  Sometimes I could move the steering wheel quick or flick an scv quickly to make it quit but the warmer the oil the worse it acted up.  It was the check valve RE264764 in the load sense line coming from the pump to the rear hitch frame.  After replacing it, pressures would immediately go from high to resting LS pressure after any function was used.