Well, I found a culprit. More specifically, TWO culprits.
The first was a wet rag in the trunk with what smells like antifreeze on it.
The second was MUCH bigger.

The sound deadening material that sits on the back package shelf is saturated. Not soaked,
saturated!
I pulled that b**** out and now its spinning around in the dryer (don't worry, I'm supervising it since I have NO idea what this stuff is made of and it might catch on fire).
This probably happened because I do drive the car around in the rain with the top down. The freeze/thaw cycles of winter just made the moisture much more apparent. This also goes to say that my top definitely does not leak what-so-ever since it was able to keep this moisture IN the car.
The reason the problem wasn't found before is because the carpet on the back deck is actually separated from the deadening material by a hardcore rubber mat- keeping the top carpet layer dry. Once pulled back layer by layer, the problem was obvious.
