2004 Dodge Srt-4 smells a like a bird's nest or something

This is a shot in the dark. Before taking my dashboard apart, I thought I would give you guys a try. You have been helpful in the past. I aboutan '04 Dodge Neon SRT-4 with about 17K miles in jan 2009. The interior of my car has always smelled new since I bought it. In April 2009 I had to go out of town for work and I drove my car from Florida to San Antonio, TX. I parked my car at the Marriot in San Antonio and rode with co-workers to work everyday. My car didn't get driven for a week straight. I drove it some that weekend and then for a second week it sat in the parking lot. After that we changed hotels and stayed on the AF base there. When I stayed on the base I started driving my car to work everyday and. Here is where it gets interesting.

Since leaving my car at that Marriot, parked constantly for almost two weeks. Everytime I use the vents, heat, A/C, anything with air coming out of the vents it has this smell. Smells like a bird's nest, or bird's poop, or some kind of animal. It is especially strong when I first turn on the air (in any form). It doesn't matter if I used recirc air or outside air. Last night I pulled apart the outside vent (where the windshield wipers sit) and saw nothing except a few leaves, which I vaccumed out of there. I am confident the smell is coming from inside the dash somewhere, but I don't know what it is or where it's exactly coming from. I do a bunch of work on my car myself and I would have noticed a dead animal or bird's nest inside my motor somewhere.

Also, some of the other guys I was working there with brought there cars, and they had the same smell in there cars from there as well. I have had that smell in my car since that time. Air fresheners mask the smell temporarily but it always returns. Its driving me nuts. I can't stand it! Please help! Anyone have any ideas on what it could be or where to check next? Thanks!

-tyler