Think of your pipes like a straw in a fizzy drink. If you gulp too fast, you get air bubbles that make a mess. In your home, air pockets in the water lines act like tiny trampolines for the water.
When you turn off a faucet quickly, that rushing water hits the air pocket and bounces. That bounce is the loud knock you hear. The fix is as simple as burping a baby—you just need to let the air out.
To do this, shut off the main water valve to your house (usually near the street or in the basement). Then, turn on the highest faucet in your house (like a third-floor shower) and the lowest (like a basement hose bib). Let them drip until all the water stops.
Next, turn the main valve back on. The water will rush back through the system, pushing that trapped air out through your open taps. Let the water run for a minute, then close the faucets. Poof—your ghost has been exorcised.
