That is a small leak in the evaporative system that controls the fuel vapors. I would start by " smoking" the system. Since this is not a machine a d-i-yer would have, look at the fuel cap and the sealing surface of the cap. If there is a question of a poor seal, replace the cap, clean the neck surface the cap seals to and lightly coat it with vaseline. IF that doesn't resolve it, your best to take it into a shop that is capable of troubleshooting this. If you do, make sure the tank is between 1/4 to 3/4 full or the test for the evap will not run.