Hi guys, the last two posts seem like deja vu. I had the same problem. I removed the headliner because of the wire noise. In addition, when I rebuilt my tv box, I had most everything out, but did not remove the floor. I did find from underneath, that there was some kind of wood support. My steel roof used to rattle too. I eliminated most of it by siliconing the wires to either the roof or the head liner. I then judiciously used spray foam insulation, AND ran a few screws thru the roof into whatever solid wood I found.
I also had another 'wire noise'. In the curved gray vertical panel behind the dr. seat, and in the front of the coach, I found about 50' of unused wire, that was for the rear camera. It was just laying/hanging there, shaking around. I got annoyed at that and cut out all the excess, leaving a short piece of slack, then soldered the wires back together. I then (of course) silicone and ziptied it in place. Ahh...one less noise!!
btw, I wrapped all of the loose interior parts of the microwave in bubble wrap.