Growling vibration in bobcat 863

[Sophiedoc]

Used machine with about 1800 hrs.On using hydraulics for lift,dump or accessory there is a growling sound and vibrations you can feel especially well in the lift cylinders most noticeable @ low rpm.Hydrostatic drive seems OK.Hydraulic pressure on outlets tops 3000psi.We can find no air leaks down to the pump inlet or any blockage.Is there anything other than the pump that could cause this and if the pump is the culprit must it be fixed @ this stage since functioning seems OK.Thanks for any possible insight of the problem.-PS,we have replaced the hydraulic fluid also but no change.