I've read some of the other posts re: vibrating pipes and "Hammering" pipes but haven't seen anything re: "Harmonic Pipes."

My home is 9 years old & last November I had to have a new preassure valve installed. Several days later I also decided to have a re-circulator installed to have almost instant hot water available in the morning to avoid the 3 minute wait for hot water to get to the master bath.

In any event, shortly after having the recirculator installed, the pipes started to make this very loud harmonic noise that can be heard all over the house. Well, lickety split I called the plumber & was advised that what I needed was to have an expansion tank installed. (not required by code in my area)

After the install of the expansion tank we had several days of the dreaded harmonic noise but it resolved on its own. However, just about 14 days ago the harmonic problem returned. I called the same plumber who came out to fix it. After hearing the noise he determined I needed a new replacement expansion tank. After obtaining a new replacement he removed the old one & installed the new one. Only problem, it didn't fix the harmonic problem. Then he went to the preassure regulator valve, after turning the water on to create the harmonic sound he was able to grasp the valve with his hand to silence the harmonic noise.

With that, he determined something was defective with the valve he installed so he replaced it. As soon as he replaced it, harmonic problem solved. Now, 6 days later it has returned worse than ever.

Does anybody know what could be causing this terrible noise every time the water is turned on?

Help!