Noisy Vibrate Switch

So recently I traded my black iPhone 4 for someone's white iPhone 4, and everything appears fine on the outside (apart from a couple scratches on the bezel), but I noticed that when I flip the vibrate switch..there's quite a loud rattling noise.

I can tell the phone has been opened because of the slight gauges out of the screw heads..the only thing is I don't know why it was opened.

That being said. Does anyone know any remedies for a noisy vibrate? It doesn't seem to change no matter what part of the phone I'm holding.