I'm trying to help a friend diagnose his backhoe problem, I'm not sure of the year may be 2007ish it has 3000 hrs on it, he bought it 2 years ago. The noise started one day and has been there since, it doesn't do it all the time but most of the time while moving any function you will hear it. Its coming from under the cab and sounds like (banging a chain on pipes mixed in with slight whining) when it hits hard its scary loud and pulsates the function you are using, other times the function has normal speed and is quiet. I've seen similar events with uneven spring pressure inside a flow divider, but I'm not familial with this cat system. He is ready to change the pump but not knowing what else is in the hydraulic schematic I not sure that would fix it. It does this with NO load on the hydraulics, front bucket or hoe, any suggestion would be greatly appreciated
Check relief valve for either weak spring or debris IIRC all 420s are closed circuit so it could be the controller that runs the swash plate If it operates normally for a period of time its probably not the pump that said if the controller or relief valves are not working correctly it can take out the pump but i wouldn't throw a pump at it till i established that the relief valves were working correctly otherwise you will not solve the problem
Could be cavitation noise because you have suction restriction, case drain line plugged. Find the case drain hose on the pump, if it’s pulsating violently it means one of the pistons lost its slipper.