Water pipes can be noisy for many different reasons. Hot water pipes are usually the culprit. There are two primary reasons for pipes to make noise, one is that they are simply not firmly in place behind your walls. There is much pressure going through these pipes which causes them to move slightly. After a few years they can loosen up enough to bang something when water is flowing through them at high speeds. You’ll easily be able to tell if this is the problem, you’ll hear loud banging whenever you have the water on.
The other primary reason for water pipe noise is something called a water hammer. When you shut off a tap the pressure change in the pipes can cause a loud bang, that’s the water hammer. The problem in these cases is actually a lack of air. There are pockets of air in the pipes that cushion the fast-flowing water as it comes to a quick-closing valve, such as those in a toilet or washing machines.
Bob Vila’s website’s message board should give you some useful tips to quieting your noisy pipes.
http://www.bobvila.com/wwwboard/messages/38285.html
