I pulled all my door panels off this weekend for some sound proofing and I noticed two foam cones that were glued/stuck on the door to stop vibration on the plastic panel. They both fell off, on both sides, without me touching them. There is a decent chance maybe one or both of yours came loose? I've only had my car for a few weeks so that's the only thing I can think of besides some loose change, and I'm sure you looked!