u/Consistent_Pear7598

So I’m pretty desperate to figure out this issue. Our pipes started singing last May anytime we turned on the hot water to our showers. Brought in a plumber and after a difficult diagnosis he ultimately replaced an outdoor hose bib and valve, a pressure regulator valve, backflow preventer, and our main shut off (turns out it started leaking). The problem went away. Well the siren sound is back but now it starts anytime we flush a toilet, run the dishwasher, or even turn on the kitchen sink. It is so loud you can hear it outside of the house. It’s literally like a tornado siren. Brought in a plumber again and they said our expansion tank was leaking and some of the pipes leading from the hot water tank were poorly installed/could be contributing to vibrating of the hot water pipe in the laundry room/hot water heater room. They replaced that stuff yesterday but the sound is still there and even louder! I’m at my wits end. I’m picking up a water pressure gauge today to see if our PRV failed but it’s only a year old. Does anyone have any ideas on what could cause so much noise?