What does it sound like? My Yanmar 2420D has almost no hydraulic function. When you raise the engine speed above idle the line exiting the hydraulic pump just buzzes with vibration. The buzzing feeling is way less when you touch the pump or the power steering proportioning valve the line connects to about a foot away but they are firmly mounted. From the diagrams I have I don't think the pump has a relief in it. I have recently clean the strainer and changed the filter with one that fits but has a much smaller micron rating. The fiter is on the suction side of the pump. I have been waiting for weeks for the correct filter from an online source but that's another story. When the hydraulics get really warm the lines jerk like the fluid is going though in spurts and when the loader does work it's motion is often quite jerky. Help, this is turning into the gray market nightmare people speak of. Any suggestions would be seriously considered and appreciated, thanks.