Lexus RX 2004-09 :: AC / Heater Making A Smell Like Dust

So my AC has been making a smell that smells like dust. I searched the forum and found threads about mold, but this isn't a mold smell (or at least what I think mold smells like). I thought it was because I was using charcoal cabin filters but I just bought a new plain filter and I get the same smell. The smell usually happens when I first turn on the car and then goes away after 10 minutes or so and the smell almost always happens when I go through the carwash.