My wife's MCS (06 w/ 13,000,sunroof) has developed a strong musty smell on first opening of the day. It stays in town (DC) all the time, about 1/3 in a covered garage. I have been unable to find any evidence of leakage. Anyway, there has been little rain. Could this be from a cabin air filter, or similar? I'm not yet mechanically intimate w/ the car yet as its still on warranty. Maybe this is a warranty item?

 

I'd check out the carpet for water damage , maybe it was caught in the rain with the top open ....