My Faema Faemina's safety valve has started making strange noise when it heats up. In the past, it would gurgle, hiss, then settle into a quiet state of being. Now, the safety valve makes this low, throaty growl that rarely ends. When it does stop, it comes back after 30-60 secs. I checked the ball and spring, they're fine. I changed the gasket at the base. Anyone have any suggestions as to what might be causing this and how I might repair it? Thanks!

Sounds pretty normal. Turning down the pressure probably will lessen this. Compare yours to this video and maybe post your own video.
Here's a video of my own Faemina which I picked up from Orphan Espresso after they refurbished it.