If it was just cleaned or is new, air in the impeller chamber is the most likely culprit, this should go away within a few days, but you can also eliminate it immediately by assembling it submerged in the tank. Just disassemble it and reinstall the impeller under water. Also if the pump has a fair amount of calcium build up, vacuum pressure will degas the water, this will also put air bubbles in the pump, so if it is an older pump that has not been cleaned, this could be a cause. Besides that a worn disk or heavily scratched or damaged shaft can also cause this sort of noise.