I appreciate any help that I could get with knocking pipes. I bought a house 2 months ago and when I turn on the hot water in either of the two bathroom sinks, the pipes knock. I tried the recommendation: "Shut off the main water supply. Open up all the faucets in the home including outside hose bibs, etc. They only have to be open for a minute or so. Shut everything back off and turn the water supply back on."