Thanks for the replies. The smell definitely comes from the vents. I am trying to figure out what exactly makes it occur but since it is intermittent, I can't figure it out yet. The other day my son said that it smelled pretty bad and I had to turn off the heat and open the windows. Usually it happens when the heat is on and the AC light is on and is more apparent when I am stopped. I have my temperature set to 75. Hopefully I can pin point exactly how it happens because I went to a dealership last week and the person did not even allow my car to be seen by a technician. He said since he could not smell it at that time, he did not want to waist the technicians time. I tried to talk to him and change his mind but he would not take the car to the back so I left. I think I am going to another dealership next time.