I did not notice this on either of my two RFs (55g and variable silent).
I would imagine the only way for this to happen is if the spring spiral was rubbing against itself, or somehow getting caught on the rubber dome as its lifted up. You could open it up, lift the rubber domes and try to re-seat the spring inside, but that's a very painful process, as once the rubber domes are lifted, it tends to be very easy to misalign the spring so the capacitive switch mechanism won't pick it up properly and they will stop working.
You could also try to just use it extensively for a while more and maybe the spring under the rubber dome might move around every so slightly until it gets into a better position, but to be honest I have no idea if that's actually possible, as I don't know how much leeway the spring even has under the dome during normal operation, so this is just speculation.
EDIT: to be more precise: if I press and release the keys really slowly, I do hear (on some keys) hear a very very faint "pop", like the spring sticks a little bit and pops of or something, but it's so quiet there's no way to hear it during normal use and far from calling it a "rattle".