Something Smells...

My back patio smells like garbage. Like what you would smell in a back alley after garbage has been sitting around for awhile. Probably what a lot of New Orleans smelled like for awhile (and perhaps still does). What could it be. A visual inspection found no garbage in the area. My thoughts are that there may be a dead critter underneath the patio. I haven't looked there yet as it's not super easy to search down there. I may have to look through the slats. Do dead critters smell like garbage?