I took my car to the dealer complaining of a musty smell coming from the vents. I was told they didn't smell it but could do an A/C service for$129. I declined. Once home, I had a mechanic friend change the cabin filter, air filter, and use Wurth A/C/Heating Treatment spray. It smelled better for 1 month. Some say it is mildew on the evaporator coils. I'm not even sure how much it would cost to fix, but this SHOULD NOT happen to a car with now 33k miles on it.