A: Andy, you would make a great plumber's assistant since you included so much information with your question.

First, when plumbers look to pinpoint noisy pipe issues, the usual suspects are appliances and fixtures that turn on and off quickly. You noticed that your dishwasher was the trigger for the noise in the shower -- very good. Then you suspected that the water pressure may be higher than normal in your home -- again, a good call. Finally, you put two and two together and remembered a plumbing issue called "water hammer" that you suspect might be the problem. That is very good detective work!

From your letter, I agree that you are experiencing water hammer due to high water pressure combined with a dishwasher that is shutting off quickly. When the water is abruptly stopped, the "high" pressure in the pipes has to go somewhere -- and it appears to be rattling some loose lines in your shower.

You need to have a licensed plumber install what's called a "PRV" or "Pressure Reducing Valve" inside your home. This special valve is installed after the meter, right were the water line enters the home. Once installed, the valve can be adjusted to bring the home's water pressure down to normal levels.

Normal water pressure for a home should be about 45 - 70 psi, and anything over 80 psi is considered too high for most local codes. I suspect that you are over 80 psi -- and that might not only cause noises, but it can also stress out your plumbing system as well.

To test a home's water pressure, a "water pressure gauge" can be easily attached to any outside faucet. Then, you turn on the outside faucet when nothing else is running in the house, and check the gauge. If it reads over 80 psi, then you need to have the PRV installed.

In most cases, once the pressure is lowered, the water hammer noises will soften or stop completely. If not, another plumbing control called a "water hammer arrestor" can also be installed by the plumber. An arrestor is about the size of a baseball, and it contains a pressurized air pocket that absorbs water line energy.

Another good tip is installing "pipe clips" to secure the loose water lines. From what I've seen, or should I say "heard" with noisy pipes, doing one or all of the above mentioned fixes should turn your water hammer into a wiffle bat.