I have a well pump and whenever the pump kicks on, the water supply line (PVC) in the basement that leads from outside to the tank will make a loud bang noise. This occurs at a 90 in the line. I thought it might be air in the line as if the foot valve at the well pump is bad but I don't get any air come out when I turn on the faucets. I have researched "water hammer" but that mostly refers to when a faucet is turned off. How do I remedy this? Most annoying plus I don't want my PVC water line break.