[CenterIsl]

I had the same problem, and a quick search of the forum turned up others with the problem saying it was the vent tube. I don't understand the exact details, but for some it was a fuel filling switch inside the neck that fails, leaving the vent tube open during operation (normally it's cut off). They fixed the switch / valve (I think some called it the "carbon control valve") and it went away, or they stuffed something in the tube to alter the noise.

Well, my car (also a 2003 S) had the same symptoms, and blocking the vent hole when not filling did reduce the sound somewhat. But my mechanic found that the tube was misrouted and being pinched - when he fixed _that_ the sound went away almost completely. I say almost completely, because I've discovered that it does come back periodically, and I think it has something to do with the fuel filler cap not being _completely_ tight. When I give that another turn past the ratchet, it seems to go away completely.