Fuel Fume Odor - ? Help

I have a 2004 Santa Fe, 2.7, 150,000 miles. Have had the car for a month or so. I notice that at times I am getting a strong fuel odor when sitting at idle with the windows down. Why the odor, what should I look at, and is this normal? I don't always smell it, does not have to be a full tank to smell it. No fuel leak that I can see . . . I would think the canister would capture the odor?

Suggestions would be appreciated.

Chris