when i first bought mine it smelled this way too. i ripped out the carpet thinking it was moldy (which it was) and tossed it. still had the smell a few weeks later. long story short,
i took my dash apart and removed all the vents and ducts and cleaned them thoroughly with scolding hot water and bleach. I even sprayed hot water and bleach into the duct work i couldnt remove... turned the heat on and let it run for an hour to help evaporate water. i have not had the smell since.