Sometimes, especially after it rains or when its very humid, I get a musty smell inside the cab. Once I turn on the AC or drive with the windows open, the smell goes away permanently, and will come back only when its humid again. This happens mostly in the summer. I almost never use the AC, and when I leave the truck, all the windows are closed and the air selector is set to pull in outside air. The ac smells fine by the way so its not the HVAC system Does anyone know what can cause it? Is water getting into the cab somehow? I've never noticed a wet carpet or a puddle or anything. Thanks everyone.