Never mind. A couple of minutes on Google found this from Ruger's FAQ. Apparently it's a known, normal annoyance.
"Sometimes when I shake my Ruger LCR revolver, I hear a slight rattle; is that normal?
Like all newly manufactured Ruger revolvers, your LCR has a transfer bar safety system as part of the fire control mechanism. As a result, a hammer blow can be transmitted to the firing pin only when the trigger is pulled all the way to the rear. This is a positive internal safety feature. By design, the transfer bar is allowed some movement within the fire control mechanism so that trigger pull is not affected. Due to this necessary "play" in the transfer bar, a shooter will sometimes hear the transfer bar "rattle" when the revolver is shaken. This rattle caused by the play in the transfer bar is completely normal in the LCR."