Plastic Smell in a Humidor?

I have a humidor that has had a strange plastic smell in it since I bought it. I need to remove the smell before I humidify it and load it with cigars. I have tried airing it out for a few days, but once I closed it back up, the smell returned. Right now I have a box of baking soda in it with a fan blowing air into the box. I have been doing this for about a day now and the smell is still there. What other stuff can I try? Mind you that I cannot use harmful chemicals because of the cigars.