I don't know if it's a one-off, but the 350 I got from Maverick is ridiculously loud. It's not the noise of the motor, it's a very loud buzzing noise.
In some instances, the hum can be traced back to another component on the same PSU 12VDC rail that the pump isn't happy with or the PSU filtering is a little weak.
In two similar cases working with people, they had the 12VDC rail and the 5VDC rail cross talking while wired to the pump. That hum was really present in both cases until we figured that the proper wiring wasn't done with the molex to the PSU. When corrected, the noise went away.