Whenever the cold water is turned off abruptly (toilet or sink faucet, and when the sprinkler valves shut), we get a large amount of water hammer or banging pipes. I have not noticed any noise when shutting off the hot water. This problem just surfaced since doing our landscaping and adding on to our sprinkler system two months ago. There was no hint of noise prior to this. All plumbing for the additional sprinklers was done external to the house and connected to the existing system. Any ideas on how to cure the noise? The house is 35 years old and in the SF bay area.