Oktay, I did as you said and I don't *think* I have the rattle you describe.
But I honestly don't know if it's an issue, I think it may be the vibration mechanism itself. Perhaps they come from different manufacturers and one simple shakes more than the other. To my knowledge, vibration mechanisms vibrate by moving a weight back and forth through either an offset gear or an electrical switch that moves a metal weight back and forth. So the rattle itself is the vibration mechanism. Seems to me it's doing what it's intended to do.
If I heard something rattling when I picked my phone up I would be worried, as that might indicate something is loose or broken in the device. But as for thinking a device rattles too much when it vibrates may be a subjective response to the vibration feature of the phone.