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Assuming that your fuel cap is a Genuine Porsche or equivalent...It sounds to me like the howl is being produced during the purge phase. Let me explain what needs to happen during that phase. First the canister vent (purge) valve pulses, the charcoal canister shutoff valve (aka fresh air valve) opens, and the ORVR valve remains closed. Outside air is sucked through the canister shutoff valve, through the charcoal canister, through a bunch of plastic tubes by the purge valve, allowing the intake manifold to "suck" on this evaporative emission system. That howl is a result of something not seating in the system, or possibly the canister having some strange resonance producing ability. You may want to try removing the right headlight and the right front wheel housing liner where you can see the tubes connecting the filler neck to the charcoal canister. Let the car warm up, then listen to each component closely with a mechanics stethoscope. Also listen to the purge valve... This is going to be a feather in your cap if you can figure it out.
- Casey
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