Grrrr....Woo-Woo Noise From Fuel Filler Door is Back.

[Need_for_speed]

UPDATE: the noise has nothing to do with any of the bodywork. It's definitely the infamous woo - woo from the fuel filler. We made an ice cream run last night (Frosty Freeze! It's a tradition here in Newport...) and the ghost in the machine was as loud as ever.

I'm trying to understand how this evap system works to help in troubleshooting. Here's what I think I know. Please correct me if I'm wrong.

My understanding is that the DME controls when the venting of the carbon canister occurs -- I think I read somewhere that the first attempt is around 250 seconds after engine start. When venting is commanded, the regeneration valve under the intake manifold will open along with the valve controlling the carbon canister, thus allowing vacuum pressure to vent fuel vapors from the canister into the intake. Additionally, another valve opens that allows fresh air to enter the canister and refresh the carbon. After a purge cycle is complete, these valves will then close until the DME commands another purge. Later this evening, after an adult beverage, I'm going to attempt to determine which valve does what.

Anyway, here's what I think is happening: the first (and loudest) woo-woos occur just a few minutes after we're rolling down the road. They then occur very intermittently every few minutes thereafter. They become quieter as time goes on. My guess is that one of the aforementioned valves doesn't close or seat properly at the end of a purge cycle, and as the cycle repeats, the valve starts to free up and seats a bit better, reducing the noise.

Let me know if I'm on the right track here, and if you folks have any suggestions as to what to try next. I'm all ears!