Pipe squeal

We have a 12 year old house that has developed a squeal when the water is turned off. No matter what faucet or toilet uses the water, about five seconds after the water is turned off there is a sharp squeal noise from the pipes. Any suggestions as to how to fix this?

squeal

My first thought would be a bad water softener, and the second possibility is a bad pressure reducing valve.

lever ballcock

Since this occurs as the pressure is building back up in the lines I would suspect you have a lever type ballcock that I would replace with a fluidmaster.