I have one bathroom sink that makes a loud knocking/vibrating noise when the hot water is turned on full blast - sometimes it starts immediately, sometimes it takes 5-10 seconds to start. It sounds like the pipe inside the wall is vibrating. It doesn't happen with any other fixture in my home, it doesn't happen with the cold water in this particular sink, it doesn't even happen if I turn on the hot water less than full blast. My home is only 13 years old, by the way. Can anybody suggest a possible diagnosis based on this info? Is this something that a handy beginner could possibly fix (I'm assuming not)? If I call a plumber, any ballpark ideas of how much is this repair going to set me back? Is this something that is going to do harm if I ignore it? Thanks in advance for any advice.