Been mentioned several times by other new LCR owners - or other Ruger - What you're hearing is the transfer bar and it is normal. It just rattles around in there beneath the hammer to make shore new Ruger owners have something to worry about.
Sorry you had trouble with your LCP. I guess I've been lucky with all my firearms purchases so far, including an LCP and PT1911 (which both have lots of people online complaining about problems). Hopefully Ruger will make it good for you and then it'll be fine from then on.
I do find it sort of ironic that you were concerned about a possible problem with your LCR yet shot it anyway.
But more directly to your question... the transfer bar rattle is perfectly normal. Be suspicious when it doesn't rattle!
Yeah, I was just poking fun at you. I didn't notice the rattle in my GP100 until after I shot it and thoroughly cleaned it too. I did clean it right out of the box, but not too thoroughly down where the transfer bar is.
My LCP is a 371-series so I guess the early problems were identified and fixed.
I'm enjoying the GP so much that I might consider selling the LCP. Maybe. It does sit well in my pocket no matter what I'm wearing. Need to find someone local with speed strips, though, or get them online. Speed loaders don't hide well in a pocket.
Worry if it STOPS rattling. Every modern DA revolver has the same rattle -- the tranfer bar (or hammer clock, depending on design) must be fit comparatively loose to function. It's the lightweight construction of the LCR that makes it more audible with the LCR than with most.
Another complaint I see frequently with the LCR is that the action will get tied up if the trigger is short-stroked during rapid fire. Big deal. This can and will happen with any DA design if the conditions are right (or wrong, depending on how you see it).