I recently had a pressure reducing valve replaced. Since then I hear a humming or even a howling sound whenever I turn on any water source. Even when the toilet is filling, it hums or howls. As soon as I turn the water off, the sound stops. The sound is loud. I checked the pressure and it is only aroun 50psi. I would appreciate any help.

Either you have a bad prv or the main valve is not open all the way. Is the prv installed in the right direction? There is a directional arrow on it.

I have same problem. I had pressure of 150PSI. I figured PRV is gone. I recently changed my PRV at the front inlet. Water pressure is 60 PSI. but, I am now getting humming noise when I turn on any faucet in the house. What is wrong?