The rotten eggs smell, according to
http://www.acdelco.com/auto-service/#VehicleSmells (which is not a GM website, and so GM cannot be held responsible for the information there), could be due to an emissions problem. There should be an emissions warranty on the Aveo - if you wanted to send me the last 8 of the VIN I could get more information on the specifics. Also, you could always contact your servicing dealership to find out more about the warranty.
Regards,
Sarah
GM Customer Service