[wmjosiah]

It got worse again and I started getting a P0455 as well (Evap System - large leak), so I bought a 996-605-213-01 and replaced it. Interestingly, the noise did not go away, but the code has not returned. I have driven it about 400 miles since replacing the valve. Previously it would come back within 100 miles after clearing it. I figured the noise and the code were two pieces of the same problem, but perhaps I was wrong.
I tied a thin piece of rag around the fuel filler hinge to keep it from getting sucked into the valve and stuck it in the hole. It doesn't block the pipe nearly entirely... but noise gone. I'd love to fix it right though, if anyone has any other suggestions. While fixing my Porsche with a rag is funny, I might prefer other methods.