KipperSarnie
Member
A thought, could the noise be cavitation as with a ships propeller?
If so it is not an air problem but a vacuum problem where the blades of the impeller create a vacuum & the noise is caused by the sound of the water rushing in to fill the void.
Perhaps just removing the sharpness from the trailing edge of the impeller blades might reduce the void / vacuum.
If so it is not an air problem but a vacuum problem where the blades of the impeller create a vacuum & the noise is caused by the sound of the water rushing in to fill the void.
Perhaps just removing the sharpness from the trailing edge of the impeller blades might reduce the void / vacuum.