Pressure reducing valve chatter

I recently bought a new home and noticed when I first turned the water on there was a sudden burst of water so I installed an expansion tank. After installing the tank it didn't seem to help so I test the water pressure and it's coming in at a whopping 160, however when I let water regulate after letting it run it would go down to about 80 so I reduced the pressure down to about 60. The problem is the pressure when nothing is running has remained at 160, so I'm thinking maybe the Pressure reducing valve is going bad. The new issue, 2 days after installing the expansion tank is that the pressure reducing valve will random chatter or vibrate for about 20 seconds. Am I right I thinking the reducing valve is going bad?

On a separate note what psi should the expansion tank be set at, it's currently at 25 should it be closer to the 60

Thanks