Plumbing Questions? Ask a Plumber for Answers ASAP
You say you turned down the pressure by turning down the main shut off valve?
When you turn the valve this will not turn down the pressure. In order to lower the pressure you need a pressure regulator.
You should not have more than 80 psi in your house a good pressure would be about 65 psi. If you have more than 80 psi and you dont have a pressure regulator then you need to install one. If you have one then you need to get a gauge you can screw on to a hose bib to check your pressure. A pressure regulator can go bad and will need to be replaced if you cant get the pressure to go down.
When the pressure is to high when you open a faucet it can make a sound as the water goes by the angle stop.
Also you can check the pressure and temperature relief valve at the water heater this my be relieving pressure and this will make a groaning sound.