[razercruze15]

Per your post, it sounds like it only happens when the engine isn't on, with heat on after sitting for awhile.

Not 100% on this, as Iv'e never had heat on for a longish time without the engine on, but I would assume it would start to smell because no air is really being conditioned.

 

[razercruze15]

Changing the cabin air filter is probably one of the easiest things to do, you can definitely do it youself.