If your strainer is on the suction side, it looks like your suction line is smaller than your pressure line. If so, you are hearing cavitation. Jump up a size on your suction line. I realize that both of your pump ports are the same size, but you will have a certain pressure loss per foot of hose for a given diameter. Suction should always be larger than pressure. Also, make sure the vent for your tank is clear. For every gallon of water you remove from the tank, 231 cu/in of air must go into the tank. If the air can't get in, you cavitate.
John