As I was driving home from work today I heard several banging sounds. At the time I figured that it was a backfire from the truck several car lengths ahead. When I got home I looked under the vehicle and there was a hose hanging down. It looks like either a windshield washing fluid hose or a vacuum hose. With a vacuum hose missing I'd expect a check engine light. Do cars now-a-days even use vacuum hoses? It was hanging out a small hole in the under panel. I pulled on it gently and it came out. WTH?
My guess its something you picked up off the road from someone else. Looks like a diy tape job holding it in.
The one hose I can think of running from back of the car to front is venting the gas tank. That said, from the funky appearance, I think @rjparker's guess is more likely.
Perhaps the condensate drain tube from the air conditioning? Is there a wet spot on or under the carpet near the firewall?
