Update... Took the advice here, and had a plumber come and take care of it. When he came out he checked the water pressure and it read 120 pounds. He installed the new back flow regulator, a pressure reducer and a new expansion tank which was bad also. They also moved my shutoff valve and replaced it with a new one to make room for the pressure valve. I bought the parts and he charged 100.00 for labor. I thought he did a nice job too and the loud rattle I had was the back flow regulator. It's totally silent now. Thanks everyone.
