873G hydraulics question

[Siteworx]

I noticed today while running the brush cutter that when turning the machine even the slightest turn I hear a whining sound. It doesn't do it all the time but most of the time. After I finished cutting I put the grapple on to move some brush and never heard the whining again. I checked the fluid level and it is good. I changed the hydraulic filter about 100hrs ago. Could this mean a pump is going out?? What do you guys think

 

[Bswwood]

I believe if you have the M-46 Sauer Sundstrand servo controlled hydrostatic pump this noise was normal under high demand, such as running a brush cutter and oil flow demand. There was an update kit to install heavier springs in the replenishing valves.