@Jc0187 my first thought was to check/change the cabin filter, but it appears you've done that with no improvement. I then thought about this thread I had read - Rodent problem. Warning graphic picture possibly being your issue. However if it was a rodent issue then I would think you'd have the smell all the time not just when using the AC. Most likely as @Mr.2.g0 mentioned it's got to be moisture/mold/etc related to the AC. Hope you get this resolved soon and let us know what was found when you do.