Most plastics off-gas for their entire existence. That is most likely what you're smelling. It can be very toxic and dangerous to your health. High quality ABS plastic off-gasses very little, if at all. Your Lego should be okay but the bag it's stored in could be a problem. I would take it outside to open it.
I attended the Minneapolis Kidsfest last night with my son. There were plenty of things to do for him but not much for the AFOLs like me.
The one thing that made it worth it for me was the good deals that could be had in the LEGO store. All Prince Of Persia sets were on DEEP discount. Nearly 70% off retail. I picked up 7573 Battle of Alamut and 7571 Fight for the Dagger for a total of $34. And thanks to Groupon, we got a good discount on admission.
Rushed to the LEGO store after work today with cash in hand. Aaagh. They didn't get their shipment yet. Ah well, at least the PAB wall was stocked with some nice stuff. Not a complete waste of a trip. I guess I should've called beforehand.