I just started getting a strange noise at start up. It sounds like hydraulic fluid going through a pressure relief valve. Is there a relief valve on a power steering system. I have heard it at start up a couple of times and on atleast 2 other times I have heard it when turning out of my driveway. Could the fluid need to be changed? I do have a plow on the truck so the front end does get a work out sometimes.

 

there is a relief if you turn the wheel all the way to the end stop. the oil will relief or dump back to sump instead of just building up more pressure. i dont know the exact number, but normally the steering pumps buildup 1000 psi or so.