What are noisy water pipes typically caused by?

A common cause of pipe noise in a home is when the pipes vibrate or rattle inside the walls. When the home was built, the plumber is supposed to install strapping around the pipe where it enters the studs in the wall or travels through the floor to prevent this. If this strapping was not secured and has fallen off (or never there to begin with) this will cause the pipe to rattle or vibrate when the water is turned on or off and cause the noise you are hearing. I don't think it is cause for alarm, but it definitely is annoying. Repairing this problem could be simple if the noise can be pin pointed. A licensed plumber should be contacted regardless.