Pump's quieter with some back pressure?

[flyboy320]

I have a Jandy 2hp single speed pump. I have downstream of the pump, a shutoff valve and I find if I turn the shutoff valve so it's about half way closed, and creating some back pressure, the pump seems to run much quieter. There still seems to be the same amount of water coming from the water jets, so I don't think it's reducing the water outflow much. Because the pump is located beside my house, I would like to run it as quietly as possible. So I'm wondering if running the pump this way can damage it, and is this a "normal" behavior for a pump?

[acroy]

I'm no expert but 'normally' pumps should run pretty quiet. Noise is usually an indication of cavitation. If it's cavitating with the valves wide open, it might not be getting enough flow on the suction side. Are all suction side valves open, all skimmers & main drain open?

Throttling it down on the outlet side is creating an artificial blockage in the line; flow must go down to an extent.