If you shake your RX100 (lightly), does it rattle?
Mine does, and I'm trying to figure out if this is normal.
Yes mine does and I suspect it's the movable lens element for image stabilization.
could also be the drop sensor.
I forgot about that. You are probably right.
Take a look at this thread: http://forums.dpreview.com/forums/read.asp?forum=1009&message=42355418
It is probably the same to what you experience. It is the whole lense unit that can move to allow the stabilization system to work.
I guess it is the same thing I asked about here (the last of my questions): http://forums.dpreview.com/forums/readflat.asp?forum=1009&thread=42236702
At first I thought something was wrong (and I still do sometimes, because it's annoying), but the camera works great so... if it ain't broke, don't fix it.
Anyway, even with the explanations I've read so far, I still believe the barrel should be tighter, not absolutely tight since it must have some play to avoid unnecessary friction, but neither so loose. I would like the barrel play to be dampened somehow as other compacts seem to do (then again, they don't have such a big lens, that might be the reason).