Hi, I am facing the same problem. The PRV is installed in the right direction. The main valve is open all the way. Any thoughts

You could have a loose washer in the main stop valve. You could have trash in the PRV valve, otherwise you have a defective PRV valve.

Hi Novice and welcome to The Plumbing Page on AMHD.
You piggybacked on a 4 year old dead thread so I gave you one of your own. Before you post look in the upper left hand corner for the date..
Noise is caused by vibration. Can you feel where it vibrates the most? Back to you, Tom