start with the filter and I think that one has a screen there too.filter is rite behind step on right side if your standing behind tractor.Doesnt cost much,just replace it and clean screen real good. good luck
there is a rubber hose that is a return hose coming from the top deck, above the rear housing, and it attachs to the main suction tube in the rear end. if this hose gets a hole in it, the main hydraulic pump will suck air causing a noisy hydraulic system. steering will act like it's not getting oil also, hard steering. you can get to this hose by removing the cover above the pto and draining the hydraulic oil to inspect it.