Wife's 2010 convertible w/51k miles has developed a loud rattle when going over any sort of (even minor) bump in road. Sounds like it is coming from the engine compartment side of the firewall on driver's side. Nothing feels loose. I know this is hard to identify without hearing it but am wondering if it may be a common problem and someone can point me in the proper direction. It doesn't sound like suspension, but more like something has just gotten loose. Any ideas?