Hi all I have a heli HFB 15 2004..4 wheel zapi

Problem being the truck will get intermittent tight steering

When operating the steering the pump does change note...when the steering goes tight the pump note sounds the same as when under normal load..it's a very simple system but I must admit this problem is giving me a headache..

Is there any pressure points that the pump pressure or orbital can be checked..iv checked king pins and steering ram and links all fine..

Any advice greatly appreciated