Ever since I put subs in the trunk the dome light housing has been rattling really bad. I'm switching from a sealed to a ported box today, so with the rattle going to get even worse I decided to attempt to fix it.
I got some blue tape to help damper the sound and went to town. This is what I did first; http://i.imgur.com/1y4rKMl.jpg
The goal was to put tape anywhere wires would potentially rattle against plastic. I also put a piece between the car and the wire harness on the roof, http://i.imgur.com/sR83aY8.jpg
Put it back in and the rattle did go down, however it was still there with the bass turned up higher. After looking in to it more I discovered the source; the plastic clip that holds the wiring harness in to the car was not a snug fit. It was loose enough to cause rattle when it shook from bass.
You have to use a fair amount of force to pull it off, but basically just grab the harness on both ends and yank on it. The plastic clip will eventually come out. Here is a pic of the harness hanging without the clip. http://i.imgur.com/JwXCy2g.jpg
Take a knife or a screw driver to lift up the little piece that is latching itself on to the harness and slide it out. The culprit is below; http://i.imgur.com/g26Lb95.jpg
Putting everything back together with tape in appropriate places to prevent wires from hitting plastic / the car, I now have zero rattle coming from the dome lights. I'm willing to bet those of you experiencing dome light rattle from muffler drone can fix it the same way. A dealer will say you need to replace the entire dome light housing, which isn't true. My dome lights are slightly loose, but that is not what was causing the rattle.
This was just a quick experiment to see if it was easily fixable. I'm going to take dynamat and put a thin layer all around where I put tape at eventually, but for now the rattle is 100% gone. Now to tackle the rattle coming from the rear window area!