I asked about the blowing bottle noise issue on the PCA tech forum and someone answered that it was probably the valve housing in the front right fender: 996 201 231 01. This part is the housing for the two valves I replaced earlier this spring to try and resolve the issue. I know one of the valves controls flow to/from the carbon canister.
Apparently, this valve housing was a known issue and a TSB for 996 models several years ago. Of course, the part retails for around $500.
So...before I empty my wallet, is there any forum experience regarding this part? Any idea what exactly could fail in the housing that could cause the noise (rubber seal, etc.)? It looks like one of the two lines leads to the grommet opening in the fuel filler door, so my hunch is that the housing has failed in such a way that the associated valve is unable to properly seal this line.