Well when mine was going out, we could only use one shower at at at time, or the water would just drip. The pipes were banging alot too. You can look up your model, the guts of the PRV should be replaceable by buying a kit. You might want to take some pressure readings just to make sure its definatley not working.
Just curious, how did all this start. Did you ever have good pressure and now you don't.
If you're gonna DIY it, replacing the guts is a good way to go. If you're gonna have someone do it, I suggest replacing the whole PRV. I paid $150 to have it dug up and replaced.
Primaries: Mojave Red (AG)
Kegs: Hibiscus Saison (AG), Orange Kolsch (AG) , Cocunut Porter
Future Brew: Wee Heavy