Gas Smell

I have a 2000 Toyota Yaris. I have on and off smelled gas from outside of the car after I turn it off, and once in a while driving with the windows down. I have had it to about three mechanics, including the dealers, they have checked for leaks, inspected the fuel lines and even tightened the gas cap, but I still smell it. Yesterday I tracked it down to the front wheel, but once I also smelled it by the gas tank, what could it be? :banghead:

gas?
if you mean a slightly eggy/sulphurous smell, that's your cat.
it's normal.