I am inclined to beleive that this is a hydraulic pump problem.
When the pump runs for no good purpose it sounds like there is air in the fluid, ie noisy fluid movement.
I think if I get no answers my first move is to check all filters. I mostly suspect that there is a pickup problem, a partially blocked suction filter.
Biggest problem with that is this machine is new to us. Never had a Komatsu before so some info on where they all are would be appreciated. I don't want to pull apart areas where there are no filters.
I would rather not disturb anything I don't have to untill it's working with no errors......