So I'm hearing a thudding rattle. I've crawled around underneath and can't find anything loose. A mechanic checked out my front end and said things are fine. The noise seems to be coming from beneath the firewall. Up against the firewall I have what looks to me like a hose connector with nothing going to it. I'm wondering if a hose or pipe has come disconnected and fallen down where I can't see it? This photo is looking at the driver's side of the firewall. Any idea what (if anything) should be attached here?