"Phil Kangas" wrote in message
...
If you have the noise problem with the valve in neutral,
you
have either a port plumbing issue or a spool problem, the
hp line vibrating like that, suggests a back pressure
problem.
Try running with the hp hose returning into the tank.

Tom

Do you know if you have/need an open center control valve?
Sounds to me like you have a closed center valve and the
pump is relieving itself at max pressure all the time.
Phil

I have an open center bypass (safety) valve and an open center control
valve.
When the valves are centered, the pump circulates to the tank at essentially
zero pressure.

My pressure gauge is on the HP line, on the pump side of the control
valve -- so I can see the pressure the pump is delivering, rather than the
working pressure at the cylinder.

The system makes a "screech" when the relief valve opens under full
pressure. That I expect, and don't have a problem with the intermittent
noise. The noise I'm fussing over is continuous while the pump is running
at zero pressure -- just recirculating.

The pump doesn't appear to be cavitating. I've installed a much larger
return filter than necessary, and the intake screen to the pump is clean.
I'm running a low-vis oil comparable to the newer Ford tractor gearcase/lift
oils (about 5W-20 equivalent). Those oils run quieter than the older
straight-30 I used to use. Also, FWIW, the pump is NOT submerged in oil,
but a free-in-air design mounted on a motor-mount plate.

However, as in my original post... it's not the direct noise from the pump
and motor. I've suppressed that with earthworks and drywall. It's the
"ringing" of the HP line and press frame I'm trying to eliminate.

LLoyd