I had the same problem in my passenger side door, any time the midbass was hitting heavy, there would be an annoying rattling inside the door. If I pushed on the door handle, it would go away. I tried adding deadener inside the door panel, but that didn't really help.
What finally fixed it was to take some 3/4" closed cell foam weather strpping, cut it into 1.5-2" pieces, and apply it around the door lock/opening lever area. Then I took a couple more pieces and shoved them underneath the connecting cables for the lock/opening lever. No more rattling.