Thought I'd share: for quite some time a random rattling was coming from the trunk area in my X; it wasn't frequent, but still annoying, esp. since it was random and wasn't limited to just only bumps from potholes or sudden stops. Well, after multiple inspections, emptying the trunk, knocking on every body trim panel, f-bombs, etc., it was discovered that screws on one of the "engagement hooks" (as per realoem) of the floor cover came loose, and one actually came off and felt in the load tray. Tightening everything up (screws on the other hook were coming loose too) fixed the issue.