The pump will make noise when the engine is off since it is not pumping any oil. As the gears brake vacuum you will hear it. When the car is on, and oil is moving through, the pump is rather quiet.
I had tested a pumps function a long time ago and I set it up to move oil from one bucket to another...the pump just hums where there is a full load of oil going through it, but when it is just a trickle, it will make noise. Just not enough oil in the gear housing.
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