I recently had to change a DR Hi Beam A string because it was rattling. I think the windings had loosened from the core. That was on my fretless, so it wasn't fret buzz.
I actually suspected a problem with the truss rod, but changing the string solved the problem.
But that doesn't mean that the same thing happened to your strings. In your case adjusting the action might do the trick. At least if you're changing from another type of strings with different characteristics.
Hopethis helps.
