My pipes are rattling.

We had an issue about a week ago with our faucets moaning anytime the water was cut on. My husband lowered the water pressure at the mainline. Ever since then we are having an issue with our pipes rattling. And it's not as much a rattling as a bunch of sharp tapping noises in a row. Then it just stops. Here's where it gets wierd. They don't do this when the faucets are turned on and off, or when a toliet is flushed. They rattle at random times. But they ALWAYS rattle bettwen 5 and 6 AM when no one is awake. It has woken me up every morning since this past Saturday. I'm not sure what needs to be done. Does anyone have a clue what this could be?

Update: My husband just told me that he believes the actual noise is coming directly from the main line. (Where it comes into the house).

Did he adjust the PRV valve?

If yes how old is your home?

Sorry, I had to ask him. Yes he adjusted the PRV valve.
Our home was built in 2000.

Take a pressure reading. It sounds like the PRV might be failing.