Water pipes that make a lot of noise when people run water can be caused by high water pressure, loose mounting straps or even a water hammer. Troubleshooting a water system is an important part of home maintenance because a leak is one of the most expensive scenarios that happens within a home.
If a system's water pressure is too high, the pipes will bang when the water is turned on. Having a valve to reduce pressure or a pressure regulator to control the overall pressure is the easiest way to solve this problem. The best place to look for one of these is at the point where the main water supply line comes into the house. Most modern systems have one, but people who lack a regulator will get their money back in reduced water costs.
When mounting straps come loose, pipes have the range of motion to bang loudly. Usually, the straps are made of hooks and hangers coated in vinyl, attaching the pipes to framework. If a strap comes loose, the pipe can vibrate easily against framing wood pieces, making an unpleasant sound. Homeowners should check all the pipes within reach to ensure proper connection.
A "water hammer" is the sound one hears when a bunch of rushing water in the system hits a pipe with some sort of obstruction. The "thud" can echo through an entire home, but the proper response is to shut off the main water supply and open the faucet with the greatest of care.