why do pipes make noise when water is on

The pipes are noisy only after hot water usage. The fact that you hear the noise only when hot water is used in the shower is a clue to the source of the problem. Copper pipes expand when hot water flows through them. It's likely that the noise you hear later is the hot-water pipe rubbing against a stud, joist or support bracket as it contracts. In all but the most severe cases, the condition will not cause a leak. And it can be so hard to correct that unless you are already remodeling, the work is not warranted. You would need to remove the drywall everywhere you hear the noise, and insert a piece of foam rubber (or foam insulation) between the pipe and the framing.

One possible fix, according to mechanical contractor and PM contributor Pat Porzio, would be to switch from older-style metal clamps on your pipes to plastic one that can expand and contract a little. "Give the pipe a little room to move," he says. Whether or not this solution is available to you, however, depends on the location of the problem. "If it's in a wall," he says," there's not much you can do. "
The pipes are noisy when you turn water on, and after you shut it off.

It happens with both hot and cold water. It sounds like a water hammer problem, possibly coupled with water pipes that are not properly secured to the framing. You may also have high water pressure. Water hammer occurs when a faucet is turned off quickly rather than when it's turned on. That you hear the noise when you turn the faucet on quickly, indicates that the sudden movement of water causes pipes that are not properly secured to hit against the framing.

Lowering the water pressure, which should generally not be above 60 psi, often can reduce the hammer sound. This is accomplished with a pressure-reducing valve. If that doesn't help, have a plumber install air chambers, also called water hammer arresters. These are cushioning devices that absorb the energy caused by water movement. "It's like a shock absorber," Porzio says. As you can see from this question. Noises can also be caused by over pressurization of the plumbing system. To determine if the plumbing has too much pressure, you can pick up a water pressure gauge from the local hardware store for ~$5. 00 - $10. 00.

They are designed to attach to an standard hose bib, and can be used to measure static water pressure. If you find that the system has higher than normal pressure (between 40-65 psi is normal), then you should first make a call to your local municipality and ask what the static pressure outside your house is. If the pressure outside the house is as high as the pressure you are reading inside, then you will have to install, adjust, or repair a pressure reducing valve inside the house on the main service line (typically after the meter).

If you already have a pressure reducing valve, you can try to adjust it. If that does not work it likely means the valve is bad, and will have to be replaced. If you don't have a pressure reducing valve or the current one was found to be bad, you'll likely want to call a plumber to install/repair the valve. If you're handy enough to fix/install it yourself (with proper permits of course), then you know what to do. so get too it.